diff --git a/.changeset/modernize-trigger-event.md b/.changeset/modernize-trigger-event.md
new file mode 100644
index 00000000..594fb790
--- /dev/null
+++ b/.changeset/modernize-trigger-event.md
@@ -0,0 +1,23 @@
+---
+"@tko/utils": patch
+"@tko/binding.core": patch
+"@tko/provider.component": patch
+---
+
+Modernize synthetic event construction
+
+`triggerEvent` (exported from `@tko/utils`) now builds synthetic events using
+`new MouseEvent`/`KeyboardEvent`/`Event` constructors instead of the
+deprecated `document.createEvent('HTMLEvents')` + `initEvent(...)` path. This
+restores native side-effects in modern DOM implementations (e.g. synthetic
+clicks toggle checkbox `.checked` in happy-dom) without changing behavior in
+real browsers. `relatedTarget` is still set to the target element for mouse
+events to match the previous init-event argument list.
+
+`@tko/binding.core` event handler no longer assigns the legacy
+`event.cancelBubble = true` before calling `event.stopPropagation()` — the
+assignment is redundant on modern events and readonly on some implementations.
+
+`@tko/provider.component` now uses `Object.prototype.toString.call(node)` to
+detect `HTMLUnknownElement` rather than `'' + node`, which is immune to
+user-land `toString` overrides on custom elements.
diff --git a/.github/workflows/main-build.yml b/.github/workflows/main-build.yml
index 62f1b1f7..25ae8a36 100644
--- a/.github/workflows/main-build.yml
+++ b/.github/workflows/main-build.yml
@@ -30,12 +30,17 @@ jobs:
       - name: Verify ESM extensions
         run: bun run verify:esm
 
-      - name: Run tests
-        run: bunx vitest run
+      - name: Run tests (browser matrix)
+        run: bunx vitest run --project browser
         env:
           HOME: /root
           VITEST_BROWSERS: chromium,firefox,webkit
 
+      - name: Run tests (cli-happy-dom)
+        run: bunx vitest run --project cli-happy-dom
+        env:
+          HOME: /root
+
       - name: Upload build artifacts
         uses: actions/upload-artifact@v7
         with:
diff --git a/.github/workflows/test-headless.yml b/.github/workflows/test-headless.yml
index 89fb725d..cce9cafa 100644
--- a/.github/workflows/test-headless.yml
+++ b/.github/workflows/test-headless.yml
@@ -34,7 +34,30 @@ jobs:
         run: bun run verify:esm
 
       - name: Run Tests
-        run: bunx vitest run
+        run: bunx vitest run --project browser
         env:
           HOME: /root
           VITEST_BROWSERS: ${{ matrix.browser }}
+
+  cli-happy-dom:
+    runs-on: ubuntu-latest
+    container:
+      image: mcr.microsoft.com/playwright:v1.59.1-noble
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v6
+
+      - name: Install Bun
+        run: python3 tools/install-bun
+
+      - name: Install dependencies
+        run: bun install --frozen-lockfile
+
+      - name: Run Build
+        run: bun run build
+
+      - name: Run cli-happy-dom tests
+        run: bunx vitest run --project cli-happy-dom
+        env:
+          HOME: /root
diff --git a/builds/knockout/helpers/vitest-setup.js b/builds/knockout/helpers/vitest-setup.js
index 09fc6c89..2b2557d4 100644
--- a/builds/knockout/helpers/vitest-setup.js
+++ b/builds/knockout/helpers/vitest-setup.js
@@ -1,11 +1,19 @@
 import * as chai from 'chai'
 import sinon from 'sinon'
+import { isHappyDom } from '../../../packages/utils/helpers/test-env.ts'
 
 // Set globals that builds/knockout specs and mocha-test-helpers.js expect
 globalThis.chai = chai
 globalThis.expect = chai.expect
 globalThis.sinon = sinon
 
+// Test environment detector — used inside test bodies like:
+//   it('name', function (ctx) {
+//     if (isHappyDom()) return ctx.skip('happy-dom: reason')
+//     // ...
+//   })
+globalThis.isHappyDom = isHappyDom
+
 // Load the knockout build (sets globalThis.ko)
 import '../dist/browser.min.js'
 
diff --git a/builds/knockout/spec/components/defaultLoaderBehaviors.js b/builds/knockout/spec/components/defaultLoaderBehaviors.js
index d5f896dd..25eb57ea 100644
--- a/builds/knockout/spec/components/defaultLoaderBehaviors.js
+++ b/builds/knockout/spec/components/defaultLoaderBehaviors.js
@@ -283,7 +283,8 @@ describe('Components: Default loader', function () {
         return testTemplateFromElement('<script id="my-script-elem" type="text/html">{0}</script>', 'my-script-elem')
       })
 
-      it('Can be configured as the ID of a <textarea> element', function () {
+      it('Can be configured as the ID of a <textarea> element', function (ctx) {
+        if (isHappyDom()) return ctx.skip('happy-dom: <textarea> content parsing differs')
         // Special case: the textarea's value should be interpreted as a markup string
         return testTemplateFromElement('<textarea id="my-textarea-elem">{0}</textarea>', 'my-textarea-elem')
       })
@@ -306,7 +307,8 @@ describe('Components: Default loader', function () {
         return testTemplateFromElement('<script type="text/html">{0}</script>', /* elementId */ null)
       })
 
-      it('Can be configured as a <textarea> element instance', function () {
+      it('Can be configured as a <textarea> element instance', function (ctx) {
+        if (isHappyDom()) return ctx.skip('happy-dom: <textarea> content parsing differs')
         // Special case: the textarea's value should be interpreted as a markup string
         return testTemplateFromElement('<textarea>{0}</textarea>', /* elementId */ null)
       })
diff --git a/builds/knockout/spec/defaultBindings/attrBehaviors.js b/builds/knockout/spec/defaultBindings/attrBehaviors.js
index 2c5a0263..61830d4b 100644
--- a/builds/knockout/spec/defaultBindings/attrBehaviors.js
+++ b/builds/knockout/spec/defaultBindings/attrBehaviors.js
@@ -9,7 +9,8 @@ describe('Binding: Attr', function () {
     expect(testNode.childNodes[0].getAttribute('second-attribute')).to.deep.equal('true')
   })
 
-  it('Should be able to set namespaced attribute values', function () {
+  it('Should be able to set namespaced attribute values', function (ctx) {
+    if (isHappyDom()) return ctx.skip('happy-dom: Element.lookupNamespaceURI not implemented')
     var model = { myValue: 'first value' }
     testNode.innerHTML = [
       '<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">',
diff --git a/builds/knockout/spec/defaultBindings/optionsBehaviors.js b/builds/knockout/spec/defaultBindings/optionsBehaviors.js
index a19d5888..1262de4a 100644
--- a/builds/knockout/spec/defaultBindings/optionsBehaviors.js
+++ b/builds/knockout/spec/defaultBindings/optionsBehaviors.js
@@ -127,7 +127,8 @@ describe('Binding: Options', function () {
     expectHaveSelectedValues(testNode.childNodes[0], [4])
   })
 
-  it('Should select caption by default and retain selection when adding multiple items', function () {
+  it('Should select caption by default and retain selection when adding multiple items', function (ctx) {
+    if (isHappyDom()) return ctx.skip('happy-dom: <select> auto-selection semantics diverge')
     // This test failed in IE<=8 without changes made in #1208
     testNode.innerHTML = '<select data-bind="options: filterValues, optionsCaption: \'foo\'">'
     var viewModel = {
@@ -145,7 +146,8 @@ describe('Binding: Options', function () {
     expect(testNode.childNodes[0].options[0]).to.equal(captionElement)
   })
 
-  it('Should trigger a change event when the options selection is populated or changed by modifying the options data (single select)', function () {
+  it('Should trigger a change event when the options selection is populated or changed by modifying the options data (single select)', function (ctx) {
+    if (isHappyDom()) return ctx.skip('happy-dom: selectedIndex does not follow reordered <option>')
     var observable = new ko.observableArray(['A', 'B', 'C']),
       changeHandlerFireCount = 0
     testNode.innerHTML = "<select data-bind='options:myValues'></select>"
@@ -252,7 +254,8 @@ describe('Binding: Options', function () {
     expectHaveTexts(testNode.childNodes[0], ['', 'A', 'B'])
   })
 
-  it('Should allow the caption to be given by an observable, and update it when the model value changes (without affecting selection)', function () {
+  it('Should allow the caption to be given by an observable, and update it when the model value changes (without affecting selection)', function (ctx) {
+    if (isHappyDom()) return ctx.skip('happy-dom: element.options[selectedIndex] can be undefined')
     var myCaption = ko.observable('Initial caption')
     testNode.innerHTML = '<select data-bind=\'options:["A", "B"], optionsCaption: myCaption\'></select>'
     ko.applyBindings({ myCaption: myCaption }, testNode)
diff --git a/builds/knockout/spec/defaultBindings/valueBehaviors.js b/builds/knockout/spec/defaultBindings/valueBehaviors.js
index dcb4c54f..95528415 100644
--- a/builds/knockout/spec/defaultBindings/valueBehaviors.js
+++ b/builds/knockout/spec/defaultBindings/valueBehaviors.js
@@ -406,7 +406,8 @@ describe('Binding: Value', function () {
       expect(testNode.childNodes[0].selectedIndex).to.deep.equal(0)
     })
 
-    it('When size > 1, should unselect all options when value is undefined, null, or \"\"', function () {
+    it('When size > 1, should unselect all options when value is undefined, null, or \"\"', function (ctx) {
+      if (isHappyDom()) return ctx.skip('happy-dom: size>1 <select> does not honor selectedIndex = -1')
       var observable = new ko.observable('B')
       testNode.innerHTML = '<select size=\'2\' data-bind=\'options:["A", "B"], value:myObservable\'></select>'
       ko.applyBindings({ myObservable: observable }, testNode)
diff --git a/builds/knockout/spec/onErrorBehaviors.js b/builds/knockout/spec/onErrorBehaviors.js
index b9429055..df2e7192 100644
--- a/builds/knockout/spec/onErrorBehaviors.js
+++ b/builds/knockout/spec/onErrorBehaviors.js
@@ -110,7 +110,8 @@ describe('onError handler', function () {
     expect(windowOnErrorCount).to.equal(0)
   })
 
-  it('fires on async component errors', async function () {
+  it('fires on async component errors', async function (ctx) {
+    if (isHappyDom()) return ctx.skip('happy-dom: setTimeout errors bypass window.onerror')
     var component = {
       tagName: 'test-onerror',
       template: "<div data-bind='text: name'></div>",
@@ -135,7 +136,8 @@ describe('onError handler', function () {
     expect(windowOnErrorCount).to.equal(1)
   })
 
-  it('passes through the error instance', async function () {
+  it('passes through the error instance', async function (ctx) {
+    if (isHappyDom()) return ctx.skip('happy-dom: setTimeout errors bypass window.onerror')
     var expectedInstance
     ko.tasks.schedule(function () {
       expectedInstance = new Error('Some error')
diff --git a/bun.lock b/bun.lock
index 2cc38fb8..0dbc5630 100644
--- a/bun.lock
+++ b/bun.lock
@@ -12,6 +12,7 @@
         "@vitest/browser-playwright": "^4.1.4",
         "chai": "^6.2.2",
         "esbuild": "^0.28.0",
+        "happy-dom": "^20.9.0",
         "jquery": "^4.0.0",
         "knip": "^6.4.1",
         "playwright": "^1.59.1",
@@ -24,319 +25,292 @@
       "name": "@tko/build.knockout",
       "version": "4.0.1",
       "dependencies": {
-        "@tko/binding.component": "^4.0.0",
-        "@tko/binding.core": "^4.0.0",
-        "@tko/binding.foreach": "^4.0.0",
-        "@tko/binding.if": "^4.0.0",
-        "@tko/binding.template": "^4.0.0",
-        "@tko/builder": "^4.0.0",
-        "@tko/filter.punches": "^4.0.0",
-        "@tko/provider.attr": "^4.0.0",
-        "@tko/provider.bindingstring": "^4.0.0",
-        "@tko/provider.component": "^4.0.0",
-        "@tko/provider.databind": "^4.0.0",
-        "@tko/provider.multi": "^4.0.0",
-        "@tko/provider.virtual": "^4.0.0",
-        "@tko/utils.component": "^4.0.0",
-        "@tko/utils.functionrewrite": "^4.0.0",
-        "tslib": "^2.2.0",
+        "@tko/binding.component": "^4.0.1",
+        "@tko/binding.core": "^4.0.1",
+        "@tko/binding.foreach": "^4.0.1",
+        "@tko/binding.if": "^4.0.1",
+        "@tko/binding.template": "^4.0.1",
+        "@tko/builder": "^4.0.1",
+        "@tko/filter.punches": "^4.0.1",
+        "@tko/provider.attr": "^4.0.1",
+        "@tko/provider.component": "^4.0.1",
+        "@tko/provider.databind": "^4.0.1",
+        "@tko/provider.multi": "^4.0.1",
+        "@tko/provider.virtual": "^4.0.1",
+        "@tko/utils": "^4.0.1",
+        "@tko/utils.component": "^4.0.1",
+        "@tko/utils.functionrewrite": "^4.0.1",
       },
     },
     "builds/reference": {
       "name": "@tko/build.reference",
       "version": "4.0.1",
       "dependencies": {
-        "@tko/binding.component": "^4.0.0",
-        "@tko/binding.core": "^4.0.0",
-        "@tko/binding.foreach": "^4.0.0",
-        "@tko/binding.if": "^4.0.0",
-        "@tko/binding.template": "^4.0.0",
-        "@tko/builder": "^4.0.0",
-        "@tko/filter.punches": "^4.0.0",
-        "@tko/provider.attr": "^4.0.0",
-        "@tko/provider.bindingstring": "^4.0.0",
-        "@tko/provider.component": "^4.0.0",
-        "@tko/provider.databind": "^4.0.0",
-        "@tko/provider.multi": "^4.0.0",
-        "@tko/provider.mustache": "^4.0.0",
-        "@tko/provider.native": "^4.0.0",
-        "@tko/provider.virtual": "^4.0.0",
-        "@tko/utils.component": "^4.0.0",
-        "@tko/utils.jsx": "^4.0.0",
-        "tslib": "^2.2.0",
+        "@tko/binding.component": "^4.0.1",
+        "@tko/binding.core": "^4.0.1",
+        "@tko/binding.foreach": "^4.0.1",
+        "@tko/binding.if": "^4.0.1",
+        "@tko/binding.template": "^4.0.1",
+        "@tko/builder": "^4.0.1",
+        "@tko/filter.punches": "^4.0.1",
+        "@tko/provider.attr": "^4.0.1",
+        "@tko/provider.component": "^4.0.1",
+        "@tko/provider.databind": "^4.0.1",
+        "@tko/provider.multi": "^4.0.1",
+        "@tko/provider.mustache": "^4.0.1",
+        "@tko/provider.native": "^4.0.1",
+        "@tko/provider.virtual": "^4.0.1",
+        "@tko/utils": "^4.0.1",
+        "@tko/utils.component": "^4.0.1",
+        "@tko/utils.jsx": "^4.0.1",
       },
     },
     "packages/bind": {
       "name": "@tko/bind",
       "version": "4.0.1",
       "dependencies": {
-        "@tko/computed": "^4.0.0",
-        "@tko/lifecycle": "^4.0.0",
-        "@tko/observable": "^4.0.0",
-        "@tko/provider": "^4.0.0",
-        "@tko/utils": "^4.0.0",
-        "tslib": "^2.2.0",
+        "@tko/builder": "^4.0.1",
+        "@tko/computed": "^4.0.1",
+        "@tko/lifecycle": "^4.0.1",
+        "@tko/observable": "^4.0.1",
+        "@tko/provider": "^4.0.1",
+        "@tko/utils": "^4.0.1",
       },
       "peerDependencies": {
-        "@tko/binding.foreach": "^4.0.0",
+        "@tko/binding.foreach": "^4.0.1",
       },
     },
     "packages/binding.component": {
       "name": "@tko/binding.component",
       "version": "4.0.1",
       "dependencies": {
-        "@tko/bind": "^4.0.0",
-        "@tko/lifecycle": "^4.0.0",
-        "@tko/observable": "^4.0.0",
-        "@tko/provider": "^4.0.0",
-        "@tko/provider.native": "^4.0.0",
-        "@tko/utils": "^4.0.0",
-        "@tko/utils.component": "^4.0.0",
-        "@tko/utils.jsx": "^4.0.0",
-        "tslib": "^2.2.0",
+        "@tko/bind": "^4.0.1",
+        "@tko/lifecycle": "^4.0.1",
+        "@tko/observable": "^4.0.1",
+        "@tko/provider.native": "^4.0.1",
+        "@tko/utils": "^4.0.1",
+        "@tko/utils.component": "^4.0.1",
+        "@tko/utils.jsx": "^4.0.1",
       },
     },
     "packages/binding.core": {
       "name": "@tko/binding.core",
       "version": "4.0.1",
       "dependencies": {
-        "@tko/bind": "^4.0.0",
-        "@tko/computed": "^4.0.0",
-        "@tko/observable": "^4.0.0",
-        "@tko/utils": "^4.0.0",
-        "tslib": "^2.2.0",
+        "@tko/bind": "^4.0.1",
+        "@tko/computed": "^4.0.1",
+        "@tko/observable": "^4.0.1",
+        "@tko/utils": "^4.0.1",
       },
     },
     "packages/binding.foreach": {
       "name": "@tko/binding.foreach",
       "version": "4.0.1",
       "dependencies": {
-        "@tko/bind": "^4.0.0",
-        "@tko/observable": "^4.0.0",
-        "@tko/provider": "^4.0.0",
-        "@tko/utils": "^4.0.0",
-        "tslib": "^2.2.0",
+        "@tko/bind": "^4.0.1",
+        "@tko/observable": "^4.0.1",
+        "@tko/utils": "^4.0.1",
       },
     },
     "packages/binding.if": {
       "name": "@tko/binding.if",
       "version": "4.0.1",
       "dependencies": {
-        "@tko/bind": "^4.0.0",
-        "@tko/computed": "^4.0.0",
-        "@tko/observable": "^4.0.0",
-        "@tko/utils": "^4.0.0",
-        "tslib": "^2.2.0",
+        "@tko/bind": "^4.0.1",
+        "@tko/observable": "^4.0.1",
+        "@tko/utils": "^4.0.1",
       },
     },
     "packages/binding.template": {
       "name": "@tko/binding.template",
       "version": "4.0.1",
       "dependencies": {
-        "@tko/bind": "^4.0.0",
-        "@tko/computed": "^4.0.0",
-        "@tko/observable": "^4.0.0",
-        "@tko/utils": "^4.0.0",
-        "tslib": "^2.2.0",
+        "@tko/bind": "^4.0.1",
+        "@tko/computed": "^4.0.1",
+        "@tko/observable": "^4.0.1",
+        "@tko/utils": "^4.0.1",
       },
       "peerDependencies": {
-        "@tko/binding.if": "^4.0.0",
+        "@tko/binding.if": "^4.0.1",
       },
     },
     "packages/builder": {
       "name": "@tko/builder",
       "version": "4.0.1",
       "dependencies": {
-        "@tko/bind": "^4.0.0",
-        "@tko/binding.template": "^4.0.0",
-        "@tko/computed": "^4.0.0",
-        "@tko/filter.punches": "^4.0.0",
-        "@tko/lifecycle": "^4.0.0",
-        "@tko/observable": "^4.0.0",
-        "@tko/provider": "^4.0.0",
-        "@tko/utils": "^4.0.0",
-        "@tko/utils.parser": "^4.0.0",
-        "tslib": "^2.2.0",
+        "@tko/bind": "^4.0.1",
+        "@tko/binding.template": "^4.0.1",
+        "@tko/computed": "^4.0.1",
+        "@tko/lifecycle": "^4.0.1",
+        "@tko/observable": "^4.0.1",
+        "@tko/provider": "^4.0.1",
+        "@tko/utils": "^4.0.1",
+        "@tko/utils.parser": "^4.0.1",
       },
     },
     "packages/computed": {
       "name": "@tko/computed",
       "version": "4.0.1",
       "dependencies": {
-        "@tko/observable": "^4.0.0",
-        "@tko/utils": "^4.0.0",
-        "tslib": "^2.2.0",
+        "@tko/observable": "^4.0.1",
+        "@tko/utils": "^4.0.1",
       },
     },
     "packages/filter.punches": {
       "name": "@tko/filter.punches",
       "version": "4.0.1",
       "dependencies": {
-        "@tko/observable": "^4.0.0",
-        "tslib": "^2.2.0",
+        "@tko/observable": "^4.0.1",
       },
     },
     "packages/lifecycle": {
       "name": "@tko/lifecycle",
       "version": "4.0.1",
       "dependencies": {
-        "@tko/computed": "^4.0.0",
-        "@tko/utils": "^4.0.0",
-        "tslib": "^2.2.0",
+        "@tko/computed": "^4.0.1",
+        "@tko/utils": "^4.0.1",
       },
       "peerDependencies": {
-        "@tko/observable": "^4.0.0",
+        "@tko/observable": "^4.0.1",
       },
     },
     "packages/observable": {
       "name": "@tko/observable",
       "version": "4.0.1",
       "dependencies": {
-        "@tko/utils": "^4.0.0",
-        "tslib": "^2.2.0",
+        "@tko/utils": "^4.0.1",
       },
     },
     "packages/provider": {
       "name": "@tko/provider",
       "version": "4.0.1",
       "dependencies": {
-        "@tko/observable": "^4.0.0",
-        "@tko/utils": "^4.0.0",
-        "tslib": "^2.2.0",
+        "@tko/bind": "^4.0.1",
+        "@tko/observable": "^4.0.1",
+        "@tko/utils": "^4.0.1",
       },
     },
     "packages/provider.attr": {
       "name": "@tko/provider.attr",
       "version": "4.0.1",
       "dependencies": {
-        "@tko/provider": "^4.0.0",
-        "tslib": "^2.2.0",
+        "@tko/provider": "^4.0.1",
       },
     },
     "packages/provider.bindingstring": {
       "name": "@tko/provider.bindingstring",
       "version": "4.0.1",
       "dependencies": {
-        "@tko/provider": "^4.0.0",
-        "@tko/utils.parser": "^4.0.0",
-        "tslib": "^2.2.0",
+        "@tko/provider": "^4.0.1",
+        "@tko/utils.parser": "^4.0.1",
       },
     },
     "packages/provider.component": {
       "name": "@tko/provider.component",
       "version": "4.0.1",
       "dependencies": {
-        "@tko/computed": "^4.0.0",
-        "@tko/observable": "^4.0.0",
-        "@tko/provider": "^4.0.0",
-        "@tko/utils": "^4.0.0",
-        "@tko/utils.component": "^4.0.0",
-        "@tko/utils.parser": "^4.0.0",
-        "tslib": "^2.2.0",
+        "@tko/computed": "^4.0.1",
+        "@tko/observable": "^4.0.1",
+        "@tko/provider": "^4.0.1",
+        "@tko/utils": "^4.0.1",
+        "@tko/utils.component": "^4.0.1",
+        "@tko/utils.parser": "^4.0.1",
       },
     },
     "packages/provider.databind": {
       "name": "@tko/provider.databind",
       "version": "4.0.1",
       "dependencies": {
-        "@tko/provider.bindingstring": "^4.0.0",
-        "tslib": "^2.2.0",
+        "@tko/bind": "^4.0.1",
+        "@tko/provider.bindingstring": "^4.0.1",
       },
     },
     "packages/provider.multi": {
       "name": "@tko/provider.multi",
       "version": "4.0.1",
       "dependencies": {
-        "@tko/provider": "^4.0.0",
-        "tslib": "^2.2.0",
+        "@tko/bind": "^4.0.1",
+        "@tko/provider": "^4.0.1",
       },
     },
     "packages/provider.mustache": {
       "name": "@tko/provider.mustache",
       "version": "4.0.1",
       "dependencies": {
-        "@tko/binding.template": "^4.0.0",
-        "@tko/observable": "^4.0.0",
-        "@tko/provider": "^4.0.0",
-        "@tko/utils": "^4.0.0",
-        "@tko/utils.parser": "^4.0.0",
-        "tslib": "^2.2.0",
+        "@tko/observable": "^4.0.1",
+        "@tko/provider": "^4.0.1",
+        "@tko/utils.parser": "^4.0.1",
       },
     },
     "packages/provider.native": {
       "name": "@tko/provider.native",
       "version": "4.0.1",
       "dependencies": {
-        "@tko/observable": "^4.0.0",
-        "@tko/provider": "^4.0.0",
-        "tslib": "^2.2.0",
+        "@tko/bind": "^4.0.1",
+        "@tko/observable": "^4.0.1",
+        "@tko/provider": "^4.0.1",
       },
     },
     "packages/provider.virtual": {
       "name": "@tko/provider.virtual",
       "version": "4.0.1",
       "dependencies": {
-        "@tko/provider.bindingstring": "^4.0.0",
-        "@tko/utils": "^4.0.0",
-        "tslib": "^2.2.0",
+        "@tko/bind": "^4.0.1",
+        "@tko/provider.bindingstring": "^4.0.1",
+        "@tko/utils": "^4.0.1",
       },
     },
     "packages/utils": {
       "name": "@tko/utils",
       "version": "4.0.1",
       "dependencies": {
-        "tslib": "^2.2.0",
+        "@tko/builder": "^4.0.1",
+        "@tko/provider": "^4.0.1",
       },
     },
     "packages/utils.component": {
       "name": "@tko/utils.component",
       "version": "4.0.1",
       "dependencies": {
-        "@tko/lifecycle": "^4.0.0",
-        "@tko/observable": "^4.0.0",
-        "@tko/utils": "^4.0.0",
-        "tslib": "^2.2.0",
+        "@tko/lifecycle": "^4.0.1",
+        "@tko/observable": "^4.0.1",
+        "@tko/utils": "^4.0.1",
       },
       "peerDependencies": {
-        "@tko/bind": "^4.0.0",
-        "@tko/binding.core": "^4.0.0",
-        "@tko/computed": "^4.0.0",
-        "@tko/provider.multi": "^4.0.0",
-        "@tko/provider.virtual": "^4.0.0",
+        "@tko/bind": "^4.0.1",
+        "@tko/binding.core": "^4.0.1",
+        "@tko/computed": "^4.0.1",
+        "@tko/provider.multi": "^4.0.1",
+        "@tko/provider.virtual": "^4.0.1",
       },
     },
     "packages/utils.functionrewrite": {
       "name": "@tko/utils.functionrewrite",
       "version": "4.0.1",
-      "dependencies": {
-        "tslib": "^2.2.0",
-      },
     },
     "packages/utils.jsx": {
       "name": "@tko/utils.jsx",
       "version": "4.0.1",
       "dependencies": {
-        "@tko/bind": "^4.0.0",
-        "@tko/computed": "^4.0.0",
-        "@tko/lifecycle": "^4.0.0",
-        "@tko/observable": "^4.0.0",
-        "@tko/provider.native": "^4.0.0",
-        "@tko/utils": "^4.0.0",
-        "tslib": "^2.2.0",
+        "@tko/bind": "^4.0.1",
+        "@tko/computed": "^4.0.1",
+        "@tko/lifecycle": "^4.0.1",
+        "@tko/observable": "^4.0.1",
+        "@tko/provider.native": "^4.0.1",
+        "@tko/utils": "^4.0.1",
       },
     },
     "packages/utils.parser": {
       "name": "@tko/utils.parser",
       "version": "4.0.1",
       "dependencies": {
-        "@tko/observable": "^4.0.0",
-        "@tko/utils": "^4.0.0",
-        "tslib": "^2.2.0",
+        "@tko/observable": "^4.0.1",
+        "@tko/utils": "^4.0.1",
       },
       "peerDependencies": {
-        "@tko/bind": "^4.0.0",
-        "@tko/binding.core": "^4.0.0",
-        "@tko/provider.databind": "^4.0.0",
+        "@tko/bind": "^4.0.1",
+        "@tko/binding.core": "^4.0.1",
+        "@tko/provider.databind": "^4.0.1",
       },
     },
   },
@@ -663,6 +637,10 @@
 
     "@types/node": ["@types/node@20.19.37", "", { "dependencies": { "undici-types": "~6.21.0" } }, "sha512-8kzdPJ3FsNsVIurqBs7oodNnCEVbni9yUEkaHbgptDACOPW04jimGagZ51E6+lXUwJjgnBw+hyko/lkFWCldqw=="],
 
+    "@types/whatwg-mimetype": ["@types/whatwg-mimetype@3.0.2", "", {}, "sha512-c2AKvDT8ToxLIOUlN51gTiHXflsfIFisS4pO7pDPoKouJCESkhZnEy623gwP9laCy5lnLDAw1vAzu2vM2YLOrA=="],
+
+    "@types/ws": ["@types/ws@8.18.1", "", { "dependencies": { "@types/node": "*" } }, "sha512-ThVF6DCVhA8kUGy+aazFQ4kXQ7E1Ty7A3ypFOe0IcJV8O/M511G99AW24irKrW56Wt44yG9+ij8FaqoBGkuBXg=="],
+
     "@vitest/browser": ["@vitest/browser@4.1.4", "", { "dependencies": { "@blazediff/core": "1.9.1", "@vitest/mocker": "4.1.4", "@vitest/utils": "4.1.4", "magic-string": "^0.30.21", "pngjs": "^7.0.0", "sirv": "^3.0.2", "tinyrainbow": "^3.1.0", "ws": "^8.19.0" }, "peerDependencies": { "vitest": "4.1.4" } }, "sha512-TrNaY/yVOwxtrxNsDUC/wQ56xSwplpytTeRAqF/197xV/ZddxxulBsxR6TrhVMyniJmp9in8d5u0AcDaNRY30w=="],
 
     "@vitest/browser-playwright": ["@vitest/browser-playwright@4.1.4", "", { "dependencies": { "@vitest/browser": "4.1.4", "@vitest/mocker": "4.1.4", "tinyrainbow": "^3.1.0" }, "peerDependencies": { "playwright": "*", "vitest": "4.1.4" } }, "sha512-q3PchVhZINX23Pv+RERgAtDlp6wzVkID/smOPnZ5YGWpeWUe3jMNYppeVh15j4il3G7JIJty1d1Kicpm0HSMig=="],
@@ -713,6 +691,8 @@
 
     "enquirer": ["enquirer@2.4.1", "", { "dependencies": { "ansi-colors": "^4.1.1", "strip-ansi": "^6.0.1" } }, "sha512-rRqJg/6gd538VHvR3PSrdRBb/1Vy2YfzHqzvbhGIQpDRKIa4FgV/54b5Q1xYSxOOwKvjXweS26E0Q+nAMwp2pQ=="],
 
+    "entities": ["entities@7.0.1", "", {}, "sha512-TWrgLOFUQTH994YUyl1yT4uyavY5nNB5muff+RtWaqNVCAK408b5ZnnbNAUEWLTCpum9w6arT70i1XdQ4UeOPA=="],
+
     "es-module-lexer": ["es-module-lexer@2.0.0", "", {}, "sha512-5POEcUuZybH7IdmGsD8wlf0AI55wMecM9rVBTI/qEAy2c1kTOm3DjFYjrBdI2K3BaJjJYfYFeRtM0t9ssnRuxw=="],
 
     "esbuild": ["esbuild@0.28.0", "", { "optionalDependencies": { "@esbuild/aix-ppc64": "0.28.0", "@esbuild/android-arm": "0.28.0", "@esbuild/android-arm64": "0.28.0", "@esbuild/android-x64": "0.28.0", "@esbuild/darwin-arm64": "0.28.0", "@esbuild/darwin-x64": "0.28.0", "@esbuild/freebsd-arm64": "0.28.0", "@esbuild/freebsd-x64": "0.28.0", "@esbuild/linux-arm": "0.28.0", "@esbuild/linux-arm64": "0.28.0", "@esbuild/linux-ia32": "0.28.0", "@esbuild/linux-loong64": "0.28.0", "@esbuild/linux-mips64el": "0.28.0", "@esbuild/linux-ppc64": "0.28.0", "@esbuild/linux-riscv64": "0.28.0", "@esbuild/linux-s390x": "0.28.0", "@esbuild/linux-x64": "0.28.0", "@esbuild/netbsd-arm64": "0.28.0", "@esbuild/netbsd-x64": "0.28.0", "@esbuild/openbsd-arm64": "0.28.0", "@esbuild/openbsd-x64": "0.28.0", "@esbuild/openharmony-arm64": "0.28.0", "@esbuild/sunos-x64": "0.28.0", "@esbuild/win32-arm64": "0.28.0", "@esbuild/win32-ia32": "0.28.0", "@esbuild/win32-x64": "0.28.0" }, "bin": "bin/esbuild" }, "sha512-sNR9MHpXSUV/XB4zmsFKN+QgVG82Cc7+/aaxJ8Adi8hyOac+EXptIp45QBPaVyX3N70664wRbTcLTOemCAnyqw=="],
@@ -751,6 +731,8 @@
 
     "graceful-fs": ["graceful-fs@4.2.11", "", {}, "sha512-RbJ5/jmFcNNCcDV5o9eTnBLJ/HszWV0P73bc+Ff4nS/rJj+YaS6IGyiOL0VoBYX+l1Wrl3k63h/KrH+nhJ0XvQ=="],
 
+    "happy-dom": ["happy-dom@20.9.0", "", { "dependencies": { "@types/node": ">=20.0.0", "@types/whatwg-mimetype": "^3.0.2", "@types/ws": "^8.18.1", "entities": "^7.0.1", "whatwg-mimetype": "^3.0.0", "ws": "^8.18.3" } }, "sha512-GZZ9mKe8r646NUAf/zemnGbjYh4Bt8/MqASJY+pSm5ZDtc3YQox+4gsLI7yi1hba6o+eCsGxpHn5+iEVn31/FQ=="],
+
     "human-id": ["human-id@4.1.3", "", { "bin": "dist/cli.js" }, "sha512-tsYlhAYpjCKa//8rXZ9DqKEawhPoSytweBC2eNvcaDK+57RZLHGqNs3PZTQO6yekLFSuvA6AlnAfrw1uBvtb+Q=="],
 
     "iconv-lite": ["iconv-lite@0.7.2", "", { "dependencies": { "safer-buffer": ">= 2.1.2 < 3.0.0" } }, "sha512-im9DjEDQ55s9fL4EYzOAv0yMqmMBSZp6G0VvFyTMPKWxiSBHUj9NW/qqLmXUwXrrM7AvqSlTCfvqRb0cM8yYqw=="],
@@ -949,6 +931,8 @@
 
     "walk-up-path": ["walk-up-path@4.0.0", "", {}, "sha512-3hu+tD8YzSLGuFYtPRb48vdhKMi0KQV5sn+uWr8+7dMEq/2G/dtLrdDinkLjqq5TIbIBjYJ4Ax/n3YiaW7QM8A=="],
 
+    "whatwg-mimetype": ["whatwg-mimetype@3.0.0", "", {}, "sha512-nt+N2dzIutVRxARx1nghPKGv1xHikU7HKdfafKkLNLindmPU/ch3U31NOCGGA/dmPcmb1VlofO0vnKAcsm0o/Q=="],
+
     "which": ["which@2.0.2", "", { "dependencies": { "isexe": "^2.0.0" }, "bin": { "node-which": "bin/node-which" } }, "sha512-BLI3Tl1TW3Pvl70l3yq3Y64i+awpwXqsGBYWkkqMtnbXgrMD+yj7rhW0kuEDxzJaYXGjEW5ogapKNMEKNMjibA=="],
 
     "why-is-node-running": ["why-is-node-running@2.3.0", "", { "dependencies": { "siginfo": "^2.0.0", "stackback": "0.0.2" }, "bin": { "why-is-node-running": "cli.js" } }, "sha512-hUrmaWBdVDcxvYqnyh09zunKzROWjbZTiNy8dBEjkS7ehEDQibXJ7XvlmtbwuTclUiIyN+CyXQD4Vmko8fNm8w=="],
diff --git a/package.json b/package.json
index adf23237..d808b5a2 100644
--- a/package.json
+++ b/package.json
@@ -38,6 +38,7 @@
     "@vitest/browser-playwright": "^4.1.4",
     "chai": "^6.2.2",
     "esbuild": "^0.28.0",
+    "happy-dom": "^20.9.0",
     "jquery": "^4.0.0",
     "knip": "^6.4.1",
     "playwright": "^1.59.1",
diff --git a/packages/binding.component/spec/componentBindingBehaviors.ts b/packages/binding.component/spec/componentBindingBehaviors.ts
index 8b39cccb..266e4d8b 100644
--- a/packages/binding.component/spec/componentBindingBehaviors.ts
+++ b/packages/binding.component/spec/componentBindingBehaviors.ts
@@ -35,6 +35,7 @@ import {
   restoreAfter,
   useMockForTasks
 } from '../../utils/helpers/mocha-test-helpers'
+import { isHappyDom } from '../../utils/helpers/test-env'
 
 describe('Components: Component binding', function () {
   let testComponentName = 'test-component',
@@ -1252,7 +1253,7 @@ describe('Components: Component binding', function () {
       expect((testNode.children[0] as HTMLInputElement).innerText.trim()).to.deep.equal(`beep`)
     })
 
-    it('inserts multiple times into virtual element slot with the slot template', function () {
+    it('inserts multiple times into virtual element slot with the slot template', function (ctx: any) {
       testNode.innerHTML = `
         <test-component>
           <template slot='alpha'>beep</template>
@@ -1270,6 +1271,7 @@ describe('Components: Component binding', function () {
       }
       ViewModel.register('test-component')
 
+      if (isHappyDom()) return ctx.skip('happy-dom: innerText whitespace rendering differs from real browsers')
       applyBindings(outerViewModel, testNode)
       expect((testNode.children[0] as HTMLInputElement).innerText.trim()).to.deep.equal(`beep / beep`)
     })
@@ -1381,11 +1383,13 @@ describe('Components: Component binding', function () {
       ViewModel.register('test-component')
 
       applyBindings(outerViewModel, testNode)
+      // `innerText` varies slightly across DOM implementations around whitespace
+      // between block siblings; normalize before comparing text contents.
       const innerText = (testNode.children[0] as HTMLElement).innerText.replace(/\s+/g, ' ').trim()
       expect(innerText).to.deep.equal(`X beep Y Gamma Zeta Q`)
     })
 
-    it('inserts all component template nodes in an unnamed (default) slot', function () {
+    it('inserts all component template nodes in an unnamed (default) slot', function (ctx: any) {
       testNode.innerHTML = `
         <test-component>
           <em>B.</em>
@@ -1404,13 +1408,14 @@ describe('Components: Component binding', function () {
       }
       ViewModel.register('test-component')
 
+      if (isHappyDom()) return ctx.skip('happy-dom: innerText whitespace rendering differs from real browsers')
       applyBindings(outerViewModel, testNode)
       expect((testNode.children[0] as HTMLElement).innerText.trim()).to.deep.equal(`A. B. C.`)
       const em = testNode.children[0].children[0].children[0]
       expect(em.tagName).to.deep.equal('EM')
     })
 
-    it('inserts multiple nodes from a <template>', function () {
+    it('inserts multiple nodes from a <template>', function (ctx: any) {
       testNode.innerHTML = `
         <test-component>
           <em>B.</em>
@@ -1425,6 +1430,7 @@ describe('Components: Component binding', function () {
       }
       ViewModel.register('test-component')
 
+      if (isHappyDom()) return ctx.skip('happy-dom: innerText whitespace rendering differs from real browsers')
       applyBindings(outerViewModel, testNode)
       expect((testNode.children[0] as HTMLElement).innerText.trim()).to.deep.equal(`B. C. E.`)
       const em = testNode.children[0].children[0].children[0]
diff --git a/packages/binding.core/spec/attrBehaviors.ts b/packages/binding.core/spec/attrBehaviors.ts
index 7810dcea..632a5360 100644
--- a/packages/binding.core/spec/attrBehaviors.ts
+++ b/packages/binding.core/spec/attrBehaviors.ts
@@ -12,6 +12,7 @@ import { options } from '@tko/utils'
 import * as coreBindings from '../dist'
 
 import { prepareTestNode } from '../../utils/helpers/mocha-test-helpers'
+import { isHappyDom } from '../../utils/helpers/test-env'
 
 describe('Binding: Attr', function () {
   let testNode: HTMLElement
@@ -33,7 +34,8 @@ describe('Binding: Attr', function () {
     expect(testNode.children[0].getAttribute('second-attribute')).to.equal('true')
   })
 
-  it('Should be able to set namespaced attribute values', function () {
+  it('Should be able to set namespaced attribute values', function (ctx: any) {
+    if (isHappyDom()) return ctx.skip('happy-dom: Element.lookupNamespaceURI not implemented')
     const model = { myValue: 'first value' }
     testNode.innerHTML = [
       '<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">',
diff --git a/packages/binding.core/spec/optionsBehaviors.ts b/packages/binding.core/spec/optionsBehaviors.ts
index 89d7fe8d..e7a0b98f 100644
--- a/packages/binding.core/spec/optionsBehaviors.ts
+++ b/packages/binding.core/spec/optionsBehaviors.ts
@@ -13,6 +13,7 @@ import { bindings as coreBindings } from '../dist'
 import type { ObservableArray } from '@tko/observable'
 
 import { expectContainText, nodeText, prepareTestNode } from '../../utils/helpers/mocha-test-helpers'
+import { isHappyDom } from '../../utils/helpers/test-env'
 
 function expectArrayEqual(actual: Array<unknown>, expected: Array<unknown>) {
   expect(actual.length).to.equal(expected.length)
@@ -183,7 +184,8 @@ describe('Binding: Options', function () {
     expectHaveSelectedValues(testNode.childNodes[0], [4])
   })
 
-  it('Should select caption by default and retain selection when adding multiple items', function () {
+  it('Should select caption by default and retain selection when adding multiple items', function (ctx: any) {
+    if (isHappyDom()) return ctx.skip('happy-dom: <select> auto-selection semantics diverge')
     testNode.innerHTML = '<select data-bind="options: filterValues, optionsCaption: \'foo\'">'
     const viewModel = { filterValues: observableArray(undefined) }
     applyBindings(viewModel, testNode)
@@ -197,7 +199,8 @@ describe('Binding: Options', function () {
     expect((testNode.childNodes[0] as HTMLSelectElement).options[0]).to.equal(captionElement)
   })
 
-  it('Should trigger a change event when the options selection is populated or changed by modifying the options data (single select)', function () {
+  it('Should trigger a change event when the options selection is populated or changed by modifying the options data (single select)', function (ctx: any) {
+    if (isHappyDom()) return ctx.skip('happy-dom: selectedIndex does not follow reordered <option>')
     let myObservable: ObservableArray<string | number> = observableArray<string | number>(['A', 'B', 'C']),
       changeHandlerFireCount = 0
     testNode.innerHTML = "<select data-bind='options:myValues'></select>"
@@ -294,7 +297,8 @@ describe('Binding: Options', function () {
     expectHaveTexts(testNode.childNodes[0], ['', 'A', 'B'])
   })
 
-  it('Should allow the caption to be given by an observable, and update it when the model value changes (without affecting selection)', function () {
+  it('Should allow the caption to be given by an observable, and update it when the model value changes (without affecting selection)', function (ctx: any) {
+    if (isHappyDom()) return ctx.skip('happy-dom: element.options[selectedIndex] can be undefined')
     const myCaption = observable('Initial caption')
     testNode.innerHTML = '<select data-bind=\'options:["A", "B"], optionsCaption: myCaption\'></select>'
     applyBindings({ myCaption: myCaption }, testNode)
diff --git a/packages/binding.core/spec/valueBehaviors.ts b/packages/binding.core/spec/valueBehaviors.ts
index 363aeab3..44dd0d9a 100644
--- a/packages/binding.core/spec/valueBehaviors.ts
+++ b/packages/binding.core/spec/valueBehaviors.ts
@@ -16,6 +16,7 @@ import { options } from '@tko/utils'
 import { bindings as coreBindings } from '../dist'
 
 import { nodeText, prepareTestNode } from '../../utils/helpers/mocha-test-helpers'
+import { isHappyDom } from '../../utils/helpers/test-env'
 
 function expectArrayEqual(actual: Array<unknown>, expected: Array<unknown>) {
   expect(actual.length).to.equal(expected.length)
@@ -437,7 +438,8 @@ describe('Binding: Value', function () {
       expect(testNode.childNodes[0].selectedIndex).to.deep.equal(0)
     })
 
-    it('When size > 1, should unselect all options when value is undefined, null, or ""', function () {
+    it('When size > 1, should unselect all options when value is undefined, null, or ""', function (ctx: any) {
+      if (isHappyDom()) return ctx.skip('happy-dom: size>1 <select> does not honor selectedIndex = -1')
       const myObservable = observable('B')
       testNode.innerHTML = '<select size=\'2\' data-bind=\'options:["A", "B"], value:myObservable\'></select>'
       applyBindings({ myObservable: myObservable }, testNode)
diff --git a/packages/binding.core/src/event.ts b/packages/binding.core/src/event.ts
index 62cfb67e..94d10ec9 100644
--- a/packages/binding.core/src/event.ts
+++ b/packages/binding.core/src/event.ts
@@ -64,10 +64,7 @@ export const eventHandler = {
 
         const bubbleMark = allBindings.get(eventName + 'Bubble') !== false
         if (bubble === false || !bubbleMark) {
-          event.cancelBubble = true
-          if (event.stopPropagation) {
-            event.stopPropagation()
-          }
+          event.stopPropagation()
         }
       }
 
diff --git a/packages/binding.foreach/spec/eachBehavior.ts b/packages/binding.foreach/spec/eachBehavior.ts
index c42260c2..77e2e04e 100644
--- a/packages/binding.foreach/spec/eachBehavior.ts
+++ b/packages/binding.foreach/spec/eachBehavior.ts
@@ -26,6 +26,8 @@ import $ from 'jquery'
 
 import { assert } from 'chai'
 
+import { isHappyDom } from '../../utils/helpers/test-env'
+
 beforeEach(function () {
   const provider = new MultiProvider({ providers: [new DataBindProvider(), new VirtualProvider()] })
   options.bindingProviderInstance = provider
@@ -1025,7 +1027,8 @@ describe('focus', function () {
     assert.strictEqual(document.activeElement, document.body)
   })
 
-  it('does not preserves primitive targets when re-ordering', async function () {
+  it('does not preserves primitive targets when re-ordering', async function (ctx: any) {
+    if (isHappyDom()) return ctx.skip('happy-dom: focus()/activeElement semantics differ')
     const list = observableArray(['a', 'b', 'c'])
     applyBindings(list, $target[0])
     $target.find(':input').first().focus()
@@ -1037,7 +1040,8 @@ describe('focus', function () {
     assert.strictEqual(document.activeElement, document.body)
   })
 
-  it('preserves objects when re-ordering', async function () {
+  it('preserves objects when re-ordering', async function (ctx: any) {
+    if (isHappyDom()) return ctx.skip('happy-dom: focus()/activeElement semantics differ')
     const o0 = {}
     const list = observableArray([o0, 'b', 'c'])
     applyBindings(list, $target[0])
@@ -1050,7 +1054,8 @@ describe('focus', function () {
     assert.strictEqual(document.activeElement, $target.find(':input')[2], 'o')
   })
 
-  it('preserves objects when re-ordering multiple identical', async function () {
+  it('preserves objects when re-ordering multiple identical', async function (ctx: any) {
+    if (isHappyDom()) return ctx.skip('happy-dom: focus()/activeElement semantics differ')
     const o0 = {}
     const list = observableArray([o0, 'b', 'c'])
     applyBindings(list, $target[0])
@@ -1066,7 +1071,8 @@ describe('focus', function () {
     assert.strictEqual(document.activeElement, $target.find(':input')[3], 'o')
   })
 
-  it('preserves objects when re-ordering multiple identical, alt', async function () {
+  it('preserves objects when re-ordering multiple identical, alt', async function (ctx: any) {
+    if (isHappyDom()) return ctx.skip('happy-dom: focus()/activeElement semantics differ')
     const o0 = {}
     const list = observableArray([o0, 'b', 'c'])
     applyBindings(list, $target[0])
diff --git a/packages/binding.if/spec/elseBehaviors.ts b/packages/binding.if/spec/elseBehaviors.ts
index 5fcccd20..95da1889 100644
--- a/packages/binding.if/spec/elseBehaviors.ts
+++ b/packages/binding.if/spec/elseBehaviors.ts
@@ -15,6 +15,7 @@ import { bindings as ifBindings } from '../dist'
 import { bindings as coreBindings } from '@tko/binding.core'
 
 import { prepareTestNode } from '../../utils/helpers/mocha-test-helpers'
+import { isHappyDom } from '../../utils/helpers/test-env'
 
 describe('else inside an if binding', function () {
   let testNode: HTMLElement
@@ -31,7 +32,8 @@ describe('else inside an if binding', function () {
   })
 
   describe('as <!-- else -->', function () {
-    it('is ignored when the condition is true', function () {
+    it('is ignored when the condition is true', function (ctx: any) {
+      if (isHappyDom()) return ctx.skip('happy-dom: innerText whitespace rendering differs from real browsers')
       testNode.innerHTML = "<i data-bind='if: x'>" + 'abc <!-- else --> def' + '</i>'
       expect(testNode.childNodes[0].childNodes.length).to.equal(3)
       applyBindings({ x: true }, testNode)
@@ -39,7 +41,8 @@ describe('else inside an if binding', function () {
       expect(testNode.innerText).to.equal('abc')
     })
 
-    it('shows the else-block when the condition is false', function () {
+    it('shows the else-block when the condition is false', function (ctx: any) {
+      if (isHappyDom()) return ctx.skip('happy-dom: innerText whitespace rendering differs from real browsers')
       testNode.innerHTML = "<i data-bind='if: x'>" + 'abc <!-- else --> def ' + '</i>'
       expect(testNode.childNodes[0].childNodes.length).to.equal(3)
       applyBindings({ x: false }, testNode)
@@ -47,7 +50,8 @@ describe('else inside an if binding', function () {
       expect(testNode.innerText).to.equal('def')
     })
 
-    it('toggles between if/else on condition change', function () {
+    it('toggles between if/else on condition change', function (ctx: any) {
+      if (isHappyDom()) return ctx.skip('happy-dom: innerText whitespace rendering differs from real browsers')
       testNode.innerHTML = "<i data-bind='if: x'>" + 'abc <!-- else --> def ' + '</i>'
       const x = observable(false)
       expect(testNode.childNodes[0].childNodes.length).to.equal(3)
diff --git a/packages/binding.template/helpers/dummyTemplateEngine.ts b/packages/binding.template/helpers/dummyTemplateEngine.ts
index 8e45eb41..231d9221 100644
--- a/packages/binding.template/helpers/dummyTemplateEngine.ts
+++ b/packages/binding.template/helpers/dummyTemplateEngine.ts
@@ -50,12 +50,7 @@ export function dummyTemplateEngine(templates?) {
     let result
 
     data = data || {}
-    // Builders (e.g. rollup) mangle `data` to e.g. `data$$1`.
-    // This workaround works as long as nomangle$data doesn't
-    // appear anywhere not in tests.
     const nomangle$data: any = data
-    ;(window as any).__prevent_tree_shaking__ = nomangle$data
-    delete (window as any).__prevent_tree_shaking__
 
     rt_options.templateRenderingVariablesInScope = rt_options.templateRenderingVariablesInScope || {}
 
@@ -66,10 +61,21 @@ export function dummyTemplateEngine(templates?) {
       return renderTemplate(templateName, data, rt_options)
     })
 
+    // Bundlers can rename the closure-captured `unwrap` import (e.g. esbuild's
+    // ESM transform), breaking `eval(script)` that references it by name. Pass
+    // dependencies explicitly via `new Function` parameters so the evaluator
+    // survives any module transform. Scripts come in two flavors — a bare
+    // expression (returnable) or a statement list (no implicit return) — so
+    // try the expression form first and fall back on syntax error.
     const evalHandler = function (match, script) {
-      void unwrap // keep in scope for eval'd template expressions
       try {
-        const evalResult = eval(script)
+        let fn: Function
+        try {
+          fn = new Function('unwrap', 'nomangle$data', 'rt_options', 'bindingContext', `return (${script})`)
+        } catch {
+          fn = new Function('unwrap', 'nomangle$data', 'rt_options', 'bindingContext', script)
+        }
+        const evalResult = fn(unwrap, nomangle$data, rt_options, bindingContext)
         return evalResult === null || evalResult === undefined ? '' : evalResult.toString()
       } catch (ex: any) {
         throw new Error('Error evaluating script: [js: ' + script + ']\n\nException: ' + ex.toString(), { cause: ex })
diff --git a/packages/binding.template/spec/nativeTemplateEngineBehaviors.ts b/packages/binding.template/spec/nativeTemplateEngineBehaviors.ts
index afac54ca..f704b312 100644
--- a/packages/binding.template/spec/nativeTemplateEngineBehaviors.ts
+++ b/packages/binding.template/spec/nativeTemplateEngineBehaviors.ts
@@ -212,12 +212,12 @@ describe('Native template engine', function () {
     })
 
     it('with no content should be rejected', function () {
-      const anyWindow = window as any
-      anyWindow.testDivTemplate.innerHTML = "<div data-bind='template: { data: someItem }'></div>"
+      const testDivTemplate = ensureNodeExistsAndIsEmpty('testDivTemplate')
+      testDivTemplate.innerHTML = "<div data-bind='template: { data: someItem }'></div>"
 
       const viewModel = { someItem: { val: 'abc' } }
       expect(function () {
-        applyBindings(viewModel, anyWindow.testDivTemplate)
+        applyBindings(viewModel, testDivTemplate)
       }).to.throw(/no template content/)
     })
   })
diff --git a/packages/provider.component/src/ComponentProvider.ts b/packages/provider.component/src/ComponentProvider.ts
index 5ce60209..fe496cc2 100644
--- a/packages/provider.component/src/ComponentProvider.ts
+++ b/packages/provider.component/src/ComponentProvider.ts
@@ -59,7 +59,7 @@ export default class ComponentProvider extends Provider {
     const tagName = tagNameLower(node)
     if (registry.isRegistered(tagName)) {
       const hasDash = tagName.includes('-')
-      const isUnknownEntity = '' + node === '[object HTMLUnknownElement]'
+      const isUnknownEntity = Object.prototype.toString.call(node) === '[object HTMLUnknownElement]'
       if (hasDash || isUnknownEntity) {
         return tagName
       }
diff --git a/packages/utils.component/spec/defaultLoaderBehaviors.ts b/packages/utils.component/spec/defaultLoaderBehaviors.ts
index 6cf24538..c83dd7b2 100644
--- a/packages/utils.component/spec/defaultLoaderBehaviors.ts
+++ b/packages/utils.component/spec/defaultLoaderBehaviors.ts
@@ -5,6 +5,7 @@ import components from '../dist'
 import { expect } from 'chai'
 import sinon from 'sinon'
 import { expectContainText, restoreAfter, useMockForTasks } from '../../utils/helpers/mocha-test-helpers'
+import { isHappyDom } from '../../utils/helpers/test-env'
 
 describe('Components: Default loader', function () {
   const testComponentName = 'test-component'
@@ -279,7 +280,8 @@ describe('Components: Default loader', function () {
         testTemplateFromElement('<script id="my-script-elem" type="text/html">{0}</script>', 'my-script-elem')
       })
 
-      it('Can be configured as the ID of a <textarea> element', function () {
+      it('Can be configured as the ID of a <textarea> element', function (ctx: any) {
+        if (isHappyDom()) return ctx.skip('happy-dom: <textarea> content parsing differs')
         testTemplateFromElement('<textarea id="my-textarea-elem">{0}</textarea>', 'my-textarea-elem')
       })
 
@@ -298,7 +300,8 @@ describe('Components: Default loader', function () {
         testTemplateFromElement('<script type="text/html">{0}</script>', null)
       })
 
-      it('Can be configured as a <textarea> element instance', function () {
+      it('Can be configured as a <textarea> element instance', function (ctx: any) {
+        if (isHappyDom()) return ctx.skip('happy-dom: <textarea> content parsing differs')
         testTemplateFromElement('<textarea>{0}</textarea>', null)
       })
 
diff --git a/packages/utils/helpers/test-env.ts b/packages/utils/helpers/test-env.ts
new file mode 100644
index 00000000..7b27ced7
--- /dev/null
+++ b/packages/utils/helpers/test-env.ts
@@ -0,0 +1,10 @@
+// Detector for the vitest environment a test is running under.
+// Tests that can't run under happy-dom should guard their body with:
+//   it('name', function (ctx: any) {
+//     if (isHappyDom()) return ctx.skip('happy-dom: reason')
+//     // ...
+//   })
+
+export function isHappyDom(): boolean {
+  return typeof navigator !== 'undefined' && /HappyDOM/i.test(navigator.userAgent ?? '')
+}
diff --git a/packages/utils/spec/utilsDomBehaviors.ts b/packages/utils/spec/utilsDomBehaviors.ts
index 48d818e8..4bcb8ab7 100644
--- a/packages/utils/spec/utilsDomBehaviors.ts
+++ b/packages/utils/spec/utilsDomBehaviors.ts
@@ -5,6 +5,7 @@ import { registerEventHandler, virtualElements } from '../dist'
 import options from '../dist/options'
 import type { KnockoutInstance } from '@tko/builder'
 import { prepareTestNode, restoreAfter } from '../helpers/mocha-test-helpers'
+import { isHappyDom } from '../helpers/test-env'
 
 const ko: KnockoutInstance = globalThis.ko || {}
 ko.utils = utils
@@ -169,7 +170,8 @@ describe('selectExtensions', () => {
     testNode = prepareTestNode()
   })
 
-  it('should use loose equality for select value', () => {
+  it('should use loose equality for select value', function (ctx: any) {
+    if (isHappyDom()) return ctx.skip('happy-dom: `selected` attribute via innerHTML does not set selectedIndex')
     const select = document.createElement('select')
     select.innerHTML = `
       <option value="42" selected>Forty-two</option>
diff --git a/packages/utils/src/dom/event.ts b/packages/utils/src/dom/event.ts
index fcd8b69a..c00e1b0d 100644
--- a/packages/utils/src/dom/event.ts
+++ b/packages/utils/src/dom/event.ts
@@ -75,34 +75,29 @@ export function triggerEvent(element: Element, eventType: string): void {
 
   if (!options.useOnlyNativeEvents && options.jQuery && !useClickWorkaround) {
     options.jQuery(element).trigger(eventType)
-  } else if (typeof document.createEvent === 'function') {
-    if (typeof element.dispatchEvent === 'function') {
-      const eventCategory = knownEventTypesByEventName[eventType] || 'HTMLEvents'
-      const event = document.createEvent(eventCategory)
-      ;(event as any).initEvent(
-        eventType,
-        true,
-        true,
-        options.global,
-        0,
-        0,
-        0,
-        0,
-        0,
-        false,
-        false,
-        false,
-        false,
-        0,
-        element
-      )
-      element.dispatchEvent(event)
-    } else {
-      throw new Error("The supplied element doesn't support dispatchEvent")
+    return
+  }
+
+  if (typeof element.dispatchEvent !== 'function') {
+    if (useClickWorkaround && hasClick(element)) {
+      element.click()
+      return
     }
-  } else if (useClickWorkaround && hasClick(element)) {
-    element.click()
+    throw new Error("The supplied element doesn't support dispatchEvent")
+  }
+
+  const eventCategory = knownEventTypesByEventName[eventType] || 'HTMLEvents'
+  const view = options.global as Window | undefined
+  let event: Event
+  if (eventCategory === 'MouseEvents' && typeof MouseEvent === 'function') {
+    // Preserve the legacy initEvent(...) behavior of passing the element itself
+    // as relatedTarget — handlers for mouseover/mouseout/mouseenter/mouseleave
+    // observe event.relatedTarget.
+    event = new MouseEvent(eventType, { bubbles: true, cancelable: true, view, relatedTarget: element })
+  } else if (eventCategory === 'UIEvents' && typeof KeyboardEvent === 'function') {
+    event = new KeyboardEvent(eventType, { bubbles: true, cancelable: true, view })
   } else {
-    throw new Error("Browser doesn't support triggering events")
+    event = new Event(eventType, { bubbles: true, cancelable: true })
   }
+  element.dispatchEvent(event)
 }
diff --git a/vitest.config.ts b/vitest.config.ts
index f4964199..5b643a24 100644
--- a/vitest.config.ts
+++ b/vitest.config.ts
@@ -5,12 +5,35 @@ const browsers = ((globalThis as any).process?.env?.VITEST_BROWSERS || 'chromium
   .split(',')
   .map((b: string) => ({ browser: b.trim() }))
 
+const ALL_SPECS = ['packages/*/spec/**/*.ts', 'builds/reference/spec/**/*.js', 'builds/knockout/spec/**/*.js']
+
 export default defineConfig({
   test: {
-    include: ['packages/*/spec/**/*.ts', 'builds/reference/spec/**/*.js', 'builds/knockout/spec/**/*.js'],
-    setupFiles: ['builds/knockout/helpers/vitest-setup.js'],
-    browser: { enabled: true, provider: playwright(), headless: true, instances: browsers },
+    testTimeout: 10000,
     globals: true,
-    testTimeout: 10000
+    projects: [
+      // Authoritative real-browser matrix — UNCHANGED. Always runs every spec.
+      {
+        test: {
+          name: 'browser',
+          include: ALL_SPECS,
+          setupFiles: ['builds/knockout/helpers/vitest-setup.js'],
+          browser: { enabled: true, provider: playwright(), headless: true, instances: browsers },
+          globals: true,
+          testTimeout: 10000
+        }
+      },
+      // Additive CLI coverage — happy-dom.
+      // Intent: prove the binding engine works in a JS DOM (SSR, headless, TUI adapters).
+      {
+        test: {
+          name: 'cli-happy-dom',
+          include: ALL_SPECS,
+          environment: 'happy-dom',
+          setupFiles: ['builds/knockout/helpers/vitest-setup.js'],
+          globals: true
+        }
+      }
+    ]
   }
 })