Fix React 19 deprecation warning when accessing child ref pre-19 way (#1416)

[#1343] Fix React 19 deprecation warning when accessing child ref pre-19 way

`child.ref` is deprecated, and generates a warning in the console in R19
because refs are now first-class props.

Check the React version at runtime and if `>=19`, access it via the props;
otherwise, keep accessing it as before (a property of the child React element
object).

Author: stefcameron

.changeset/orange-bananas-laugh.md

@@ -0,0 +1,5 @@
+---
+'focus-trap-react': patch
+---
+
+Fix deprecation warning in React 19 when accessing ref the pre-v19 way

demo/js/demo-defaults.js

@@ -14,6 +14,8 @@ class DemoDefaults extends React.Component {
 
     this.mountTrap = this.mountTrap.bind(this);
     this.unmountTrap = this.unmountTrap.bind(this);
+
+    this.containerEl = null;
   }
 
   mountTrap() {
@@ -24,14 +26,24 @@ class DemoDefaults extends React.Component {
     this.setState({ activeTrap: false });
   }
 
+  // purposely using a ref here to test new React 19 "ref as a prop" behavior
+  //  with fallback to React 18 deprecated behavior
+  handleCallbackRef(el) {
+    this.containerEl = el;
+    this.containerEl?.classList.add('is-active');
+  }
+
   render() {
     const trap = this.state.activeTrap && (
       <FocusTrap
         focusTrapOptions={{
           onDeactivate: this.unmountTrap,
         }}
       >
-        <div className="trap is-active">
+        <div
+          className="trap is-active"
+          ref={(el) => this.handleCallbackRef(el)}
+        >
           <p>
             Here is a focus trap <a href="#">with</a> <a href="#">some</a>{' '}
             <a href="#">focusable</a> parts.

package-lock.json

@@ -70,8 +70,8 @@
     "@testing-library/react": "^16.1.0",
     "@testing-library/user-event": "^14.5.2",
     "@types/jquery": "^3.5.32",
-    "@types/react": "^18.3.1",
-    "@types/react-dom": "^18.3.0",
+    "@types/react": "^19.0.0",
+    "@types/react-dom": "^19.0.0",
     "all-contributors-cli": "^6.26.1",
     "babel-jest": "^29.7.0",
     "babelify": "^10.0.0",
@@ -89,8 +89,8 @@
     "jest-watch-typeahead": "^2.2.2",
     "onchange": "^7.1.0",
     "prettier": "^3.4.2",
-    "react": "^18.3.1",
-    "react-dom": "^18.3.1",
+    "react": "^19.0.0",
+    "react-dom": "^19.0.0",
     "regenerator-runtime": "^0.14.1",
     "start-server-and-test": "^2.0.9",
     "typescript": "^5.7.2"

package.json

@@ -2,6 +2,12 @@ const React = require('react');
 const { createFocusTrap } = require('focus-trap');
 const { isFocusable } = require('tabbable');
 
+/**
+ * The major version of React currently running.
+ * @type {number}
+ */
+const reactVerMajor = parseInt(/^(\d+)\./.exec(React.version)?.[1] ?? 0, 10);
+
 /**
  * @type {import('../index.d.ts').FocusTrap}
  */
@@ -391,10 +397,21 @@ class FocusTrap extends React.Component {
         const { containerElements } = this.props;
 
         if (child) {
-          if (typeof child.ref === 'function') {
-            child.ref(element);
-          } else if (child.ref) {
-            child.ref.current = element;
+          // React 19 moved the `ref` to an official prop
+          if (reactVerMajor >= 19) {
+            if (typeof child.props.ref === 'function') {
+              child.props.ref(element);
+            } else if (child.props.ref) {
+              child.props.ref.current = element;
+            }
+          } else {
+            // older versions of React had the `ref` separate from props (still works in R19
+            //  but results in a deprecation warning in Dev builds)
+            if (typeof child.ref === 'function') {
+              child.ref(element);
+            } else if (child.ref) {
+              child.ref.current = element;
+            }
           }
         }