knockout · brianmhunt · Apr 20, 2026 · Apr 20, 2026 · Apr 20, 2026 · Apr 20, 2026
diff --git a/.changeset/modernize-utils-dead-polyfills.md b/.changeset/modernize-utils-dead-polyfills.md
@@ -0,0 +1,33 @@
+---
+"@tko/utils": minor
+"@tko/utils.parser": patch
+"@tko/observable": patch
+"@tko/binding.core": patch
+"@tko/binding.foreach": patch
+"@tko/computed": patch
+"@tko/lifecycle": patch
+"@tko/builder": minor
+---
+
+Drop dead polyfill probes from `@tko/utils`
+
+Removes runtime feature detection for capabilities that all supported runtimes
+(modern browsers, Node, Bun, happy-dom) already expose unconditionally:
+
+- `functionSupportsLengthOverwrite` + `overwriteLengthPropertyIfSupported` —
+  `Object.defineProperty(fn, 'length', …)` has worked since IE9. Call sites
+  in `@tko/observable` now invoke `Object.defineProperty` directly.
+- `useSymbols` + `createSymbolOrString` — `Symbol` is always defined; call
+  sites now use `Symbol(identifier)` directly. `createSymbolOrString` is no
+  longer exposed on `ko.utils` (public API removal — minor bump for
+  `@tko/utils` and `@tko/builder`).
+- `stringTrim` + `stringStartsWith` — removed; call sites use
+  `String(value ?? '').trim()` / `value.startsWith(prefix)` inline.
+- `toggleDomNodeCssClass` SVGAnimatedString fallback — `classList` is
+  available on every supported `Element` (including SVG since SVG2).
+- `parseJson` no longer routes through `stringTrim`; it trims inline when the
+  input is a string.
+
+`packages/utils.parser/src/preparse.ts` also guards `str.match(bindingToken)`
+against the `null` return case using `?? []` — previously relied on the match
+never returning `null` for the transformed input.
diff --git a/builds/knockout/spec/bindingAttributeBehaviors.js b/builds/knockout/spec/bindingAttributeBehaviors.js
@@ -260,10 +260,6 @@ describe('Binding attribute syntax', function () {
     ko.applyBindings({}, testNode)
 
     var allowedProperties = ['$parents', '$root', 'ko', '$rawData', '$data', '$parentContext', '$parent']
-    if (ko.utils.createSymbolOrString('') === '') {
-      allowedProperties.push('_subscribable')
-      allowedProperties.push('_ancestorBindingInfo')
-    }
     ko.utils.objectForEach(ko.contextFor(testNode.childNodes[0].childNodes[0]), function (prop) {
       expect(allowedProperties).to.contain(prop)
     })

diff --git a/packages/binding.core/src/css.ts b/packages/binding.core/src/css.ts
@@ -1,4 +1,4 @@
-import { createSymbolOrString, toggleDomNodeCssClass, objectForEach, stringTrim } from '@tko/utils'
+import { toggleDomNodeCssClass, objectForEach } from '@tko/utils'
 
 import { unwrap } from '@tko/observable'
 
@@ -12,11 +12,11 @@ export const css = {
         toggleDomNodeCssClass(element, className, shouldHaveClass)
       })
     } else {
-      value = stringTrim(String(value || '')) // Make sure we don't try to store or set a non-string value
+      value = String(value ?? '').trim() // Make sure we don't try to store or set a non-string value
       toggleDomNodeCssClass(element, element[css.classesWrittenByBindingKey], false)
       element[css.classesWrittenByBindingKey] = value
       toggleDomNodeCssClass(element, value, true)
     }
   },
-  classesWrittenByBindingKey: createSymbolOrString('__ko__cssValue')
+  classesWrittenByBindingKey: Symbol('__ko__cssValue')
 }
diff --git a/packages/binding.core/src/hasfocus.ts b/packages/binding.core/src/hasfocus.ts
@@ -1,11 +1,11 @@
-import { createSymbolOrString, triggerEvent, registerEventHandler } from '@tko/utils'
+import { triggerEvent, registerEventHandler } from '@tko/utils'
 
 import { unwrap, dependencyDetection, isWriteableObservable } from '@tko/observable'
 
 import type { AllBindings } from '@tko/bind'
 
-const hasfocusUpdatingProperty = createSymbolOrString('__ko_hasfocusUpdating')
-const hasfocusLastValue = createSymbolOrString('__ko_hasfocusLastValue')
+const hasfocusUpdatingProperty = Symbol('__ko_hasfocusUpdating')
+const hasfocusLastValue = Symbol('__ko_hasfocusLastValue')
 
 export const hasfocus = {
   init: function (element, valueAccessor, _allBindings: AllBindings) {

diff --git a/packages/binding.core/src/value.ts b/packages/binding.core/src/value.ts
@@ -1,4 +1,4 @@
-import { stringStartsWith, safeSetTimeout, tagNameLower, arrayForEach, selectExtensions } from '@tko/utils'
+import { safeSetTimeout, tagNameLower, arrayForEach, selectExtensions } from '@tko/utils'
 
 import { unwrap, dependencyDetection } from '@tko/observable'
 
@@ -82,7 +82,7 @@ export class value extends BindingHandler {
     // This is useful, for example, to catch "keydown" events after the browser has updated the control
     // (otherwise, selectExtensions.readValue(this) will receive the control's value *before* the key event)
     let handler = this.valueUpdateHandler.bind(this)
-    if (stringStartsWith(eventName, 'after')) {
+    if (eventName.startsWith('after')) {
       handler = () => {
         // The elementValueBeforeEvent variable is non-null *only* during the brief gap between
         // a keyX event firing and the valueUpdateHandler running, which is scheduled to happen

diff --git a/packages/binding.foreach/src/foreach.ts b/packages/binding.foreach/src/foreach.ts
@@ -5,15 +5,7 @@
 // Employing sound techniques to make a faster Knockout foreach binding.
 // --------
 
-import {
-  arrayForEach,
-  cleanNode,
-  options,
-  virtualElements,
-  createSymbolOrString,
-  domData,
-  domNodeIsContainedBy
-} from '@tko/utils'
+import { arrayForEach, cleanNode, options, virtualElements, domData, domNodeIsContainedBy } from '@tko/utils'
 
 import { isObservable, unwrap, observable } from '@tko/observable'
 
@@ -87,7 +79,7 @@ function valueToChangeAddItem(value, index): ChangeAddItem {
 }
 
 // store a symbol for caching the pending delete info index in the data item objects
-const PENDING_DELETE_INDEX_SYM = createSymbolOrString('_ko_ffe_pending_delete_index')
+const PENDING_DELETE_INDEX_SYM = Symbol('_ko_ffe_pending_delete_index')
 
 export class ForEachBinding extends AsyncBindingHandler {
   // NOTE: valid valueAccessors include:

diff --git a/packages/builder/src/Builder.ts b/packages/builder/src/Builder.ts
@@ -17,7 +17,6 @@ import {
   cleanNode,
   cloneNodes,
   compareArrays,
-  createSymbolOrString,
   domData,
   extend,
   memoization,
@@ -116,7 +115,6 @@ export type Utils = {
   arrayRemoveItem: typeof arrayRemoveItem
   cloneNodes: typeof cloneNodes
   compareArrays: typeof compareArrays
-  createSymbolOrString: typeof createSymbolOrString
   domData: typeof domData
   domNodeDisposal: typeof domNodeDisposal
   extend: typeof extend
@@ -149,7 +147,6 @@ const utils: Utils = {
   arrayRemoveItem,
   cloneNodes,
   compareArrays,
-  createSymbolOrString,
   domData,
   domNodeDisposal,
   extend,

diff --git a/packages/computed/src/computed.ts b/packages/computed/src/computed.ts
@@ -6,7 +6,6 @@
 import {
   addDisposeCallback,
   arrayForEach,
-  createSymbolOrString,
   domNodeIsAttachedToDocument,
   extend,
   options,
@@ -28,7 +27,7 @@ import {
 
 import type { Observable, Subscribable } from '@tko/observable'
 
-const computedState: symbol = createSymbolOrString('_state')
+const computedState: symbol = Symbol('_state')
 const DISPOSED_STATE = {
   dependencyTracking: null,
   dependenciesCount: 0,

diff --git a/packages/lifecycle/src/LifeCycle.ts b/packages/lifecycle/src/LifeCycle.ts
@@ -1,10 +1,10 @@
-import { addDisposeCallback, createSymbolOrString } from '@tko/utils'
+import { addDisposeCallback } from '@tko/utils'
 
 import { computed } from '@tko/computed'
 import type { Observable } from '@tko/observable'
 
-const SUBSCRIPTIONS = createSymbolOrString('LifeCycle Subscriptions List')
-const ANCHOR_NODE = createSymbolOrString('LifeCycle Anchor Node')
+const SUBSCRIPTIONS = Symbol('LifeCycle Subscriptions List')
+const ANCHOR_NODE = Symbol('LifeCycle Anchor Node')
 
 export default class LifeCycle {
   // NOTE: For more advanced integration as an ES6 mixin, see e.g.:

diff --git a/packages/observable/src/observable.ts b/packages/observable/src/observable.ts
@@ -2,7 +2,7 @@
 //  Observable values
 //  ---
 //
-import { options, overwriteLengthPropertyIfSupported } from '@tko/utils'
+import { options } from '@tko/utils'
 
 import * as dependencyDetection from './dependencyDetection'
 import { deferUpdates } from './defer'
@@ -103,7 +103,7 @@ export function observable<T = any>(initialValue?: T): Observable {
     }
   }
 
-  overwriteLengthPropertyIfSupported(Observable as any, { value: undefined })
+  Object.defineProperty(Observable, 'length', { value: undefined })
 
   Observable[LATEST_VALUE] = initialValue
 

diff --git a/packages/observable/src/observableArray.ts b/packages/observable/src/observableArray.ts
@@ -2,7 +2,7 @@
 // Observable Arrays
 // ===
 //
-import { arrayIndexOf, arrayForEach, overwriteLengthPropertyIfSupported } from '@tko/utils'
+import { arrayIndexOf, arrayForEach } from '@tko/utils'
 
 import type { CompareArraysOptions } from '@tko/utils'
 
@@ -152,7 +152,7 @@ export function observableArray<T = any>(initialValues?: T[]): ObservableArray<T
   const result = Object.setPrototypeOf(observable(initialValues), observableArray.fn) as ObservableArray<T>
   trackArrayChanges(result)
   // ^== result.extend({ trackArrayChanges: true })
-  overwriteLengthPropertyIfSupported(result, { get: () => result()?.length })
+  Object.defineProperty(result, 'length', { get: () => result()?.length })
   return result
 }
 

diff --git a/packages/utils.parser/src/preparse.ts b/packages/utils.parser/src/preparse.ts
@@ -1,5 +1,3 @@
-import { stringTrim } from '@tko/utils'
-
 /* eslint no-cond-assign: 0 */
 
 // The following regular expressions will be used to split an object-literal string into tokens
@@ -42,7 +40,7 @@ const keywordRegexLookBehind = { in: 1, return: 1, typeof: 1 }
  */
 export default function parseObjectLiteral(objectLiteralString) {
   // Trim leading and trailing spaces from the string
-  let str = stringTrim(objectLiteralString)
+  let str = String(objectLiteralString ?? '').trim()
 
   // Trim braces '{' surrounding the whole object literal
   if (str.charCodeAt(0) === 123) str = str.slice(1, -1)
@@ -53,7 +51,7 @@ export default function parseObjectLiteral(objectLiteralString) {
 
   // Split into tokens
   const result = new Array()
-  let toks = str.match(bindingToken)
+  let toks = str.match(bindingToken) ?? []
   let key
   let values = new Array()
   let depth = 0
@@ -92,7 +90,7 @@ export default function parseObjectLiteral(objectLiteralString) {
       if (match && !keywordRegexLookBehind[match[0]]) {
         // The slash is actually a division punctuator; re-parse the remainder of the string (not including the slash)
         str = str.substring(str.indexOf(tok) + 1)
-        toks = str.match(bindingToken)
+        toks = str.match(bindingToken) ?? []
         i = -1
         // Continue with just the slash
         tok = '/'

diff --git a/packages/utils/src/css.ts b/packages/utils/src/css.ts
@@ -2,38 +2,21 @@
 // DOM - CSS
 //
 
-import { arrayForEach, addOrRemoveItem } from './array'
-
-// For details on the pattern for changing node classes
-// see: https://github.com/knockout/knockout/issues/1597
+// See: https://github.com/knockout/knockout/issues/1597
 const cssClassNameRegex = /\S+/g
 
 function toggleDomNodeCssClass(node: Element, classNames: string, shouldHaveClass?: boolean): void {
-  let addOrRemoveFn
   if (!classNames) {
     return
   }
-  if (typeof node.classList === 'object') {
-    addOrRemoveFn = node.classList[shouldHaveClass ? 'add' : 'remove']
-    arrayForEach(classNames.match(cssClassNameRegex)!, function (className) {
-      addOrRemoveFn.call(node.classList, className)
-    })
-  } else if (typeof node.className['baseVal'] === 'string') {
-    // SVG tag .classNames is an SVGAnimatedString instance
-    toggleObjectClassPropertyString(node.className, 'baseVal', classNames, shouldHaveClass)
-  } else {
-    // node.className ought to be a string.
-    toggleObjectClassPropertyString(node, 'className', classNames, shouldHaveClass)
+  const tokens = classNames.match(cssClassNameRegex)
+  if (!tokens) {
+    return
+  }
+  const method = shouldHaveClass ? 'add' : 'remove'
+  for (const token of tokens) {
+    node.classList[method](token)
   }
-}
-
-function toggleObjectClassPropertyString(obj, prop, classNames, shouldHaveClass) {
-  // obj/prop is either a node/'className' or a SVGAnimatedString/'baseVal'.
-  const currentClassNames = obj[prop].match(cssClassNameRegex) || []
-  arrayForEach(classNames.match(cssClassNameRegex), function (className) {
-    addOrRemoveItem(currentClassNames, className, shouldHaveClass)
-  })
-  obj[prop] = currentClassNames.join(' ')
 }
 
 export { toggleDomNodeCssClass }
diff --git a/packages/utils/src/function.ts b/packages/utils/src/function.ts
diff --git a/packages/utils/src/index.ts b/packages/utils/src/index.ts
@@ -8,9 +8,7 @@ export * from './array'
 export * from './async'
 export * from './error'
 export * from './object'
-export * from './function'
 export * from './string'
-export * from './symbol'
 export * from './css'
 export { default as options, defineOption, Options } from './options'
 

diff --git a/packages/utils/src/string.ts b/packages/utils/src/string.ts
@@ -2,27 +2,11 @@
 // String (and JSON)
 //
 
-export function stringTrim(string) {
-  return string === null || string === undefined
-    ? ''
-    : string.trim
-      ? string.trim()
-      : string.toString().replace(/^[\s\xa0]+|[\s\xa0]+$/g, '')
-}
-
-export function stringStartsWith(string, startsWith) {
-  string = string || ''
-  if (startsWith.length > string.length) {
-    return false
-  }
-  return string.substring(0, startsWith.length) === startsWith
-}
-
 export function parseJson<T = any>(jsonString: string): T | null {
   if (typeof jsonString === 'string') {
-    jsonString = stringTrim(jsonString)
-    if (jsonString) {
-      return JSON.parse(jsonString) as T
+    const trimmed = jsonString.trim()
+    if (trimmed) {
+      return JSON.parse(trimmed) as T
     }
   }
   return null

diff --git a/packages/utils/src/symbol.ts b/packages/utils/src/symbol.ts
diff --git a/packages/utils/src/tasks.ts b/packages/utils/src/tasks.ts
@@ -15,12 +15,7 @@ const schedulerGlobal = options.global
 
 if (schedulerGlobal && typeof schedulerGlobal.queueMicrotask === 'function') {
   options.taskScheduler = callback => schedulerGlobal.queueMicrotask(callback)
-} else if (
-  schedulerGlobal &&
-  schedulerGlobal.MutationObserver &&
-  schedulerGlobal.document &&
-  !(schedulerGlobal.navigator && schedulerGlobal.navigator.standalone)
-) {
+} else if (schedulerGlobal?.MutationObserver && schedulerGlobal.document && !schedulerGlobal.navigator?.standalone) {
   options.taskScheduler = (function () {
     let scheduledCallback: null | (() => void) = null
     let toggle = false