fix: observe container resizing in useIndexOfLastVisibleChild hook in…

…stead of window resize

src/Tabs/index.jsx

@@ -1,4 +1,10 @@
-import React, { useEffect, useMemo, useRef } from 'react';
+import React, {
+  useEffect,
+  useMemo,
+  useRef,
+  useState,
+  useCallback,
+} from 'react';
 import classNames from 'classnames';
 import PropTypes from 'prop-types';
 import BaseTabs from 'react-bootstrap/Tabs';
@@ -18,15 +24,15 @@ function Tabs({
   activeKey,
   ...props
 }) {
-  const containerElementRef = useRef(null);
+  const [containerElementRef, setContainerElementRef] = useState(null);
   const overflowElementRef = useRef(null);
   const indexOfLastVisibleChild = useIndexOfLastVisibleChild(
-    containerElementRef.current?.children[0],
+    containerElementRef?.firstChild,
     overflowElementRef.current?.parentNode,
   );
 
   useEffect(() => {
-    if (containerElementRef.current) {
+    if (containerElementRef) {
       const observer = new MutationObserver((mutations => {
         mutations.forEach(mutation => {
           // React-Bootstrap attribute 'data-rb-event-key' is responsible for the tab identification
@@ -35,8 +41,8 @@ function Tabs({
           const isActive = mutation.target.getAttribute('aria-selected') === 'true';
           // datakey attribute is added manually to the dropdown
           // elements so that they correspond to the native tabs' eventKey
-          const element = containerElementRef.current.querySelector(`[datakey='${eventKey}']`);
-          const moreTab = containerElementRef.current.querySelector('.pgn__tab_more');
+          const element = containerElementRef.querySelector(`[datakey='${eventKey}']`);
+          const moreTab = containerElementRef.querySelector('.pgn__tab_more');
           if (isActive) {
             element?.classList.add('active');
             // Here we add active class to the 'More Tab' if element exists in the dropdown
@@ -50,24 +56,24 @@ function Tabs({
           }
         });
       }));
-      observer.observe(containerElementRef.current, {
+      observer.observe(containerElementRef, {
         attributes: true, subtree: true, attributeFilter: ['aria-selected'],
       });
       return () => observer.disconnect();
     }
     return undefined;
-  }, []);
+  }, [containerElementRef]);
 
   useEffect(() => {
     if (overflowElementRef.current?.parentNode) {
       overflowElementRef.current.parentNode.tabIndex = -1;
     }
   }, [overflowElementRef.current?.parentNode]);
 
-  const handleDropdownTabClick = (eventKey) => {
-    const hiddenTab = containerElementRef.current.querySelector(`[data-rb-event-key='${eventKey}']`);
+  const handleDropdownTabClick = useCallback((eventKey) => {
+    const hiddenTab = containerElementRef.querySelector(`[data-rb-event-key='${eventKey}']`);
     hiddenTab.click();
-  };
+  }, [containerElementRef]);
 
   const tabsChildren = useMemo(() => {
     const indexOfOverflowStart = indexOfLastVisibleChild + 1;
@@ -165,10 +171,10 @@ function Tabs({
     />
     ));
     return childrenList;
-  }, [activeKey, children, defaultActiveKey, indexOfLastVisibleChild, moreTabText]);
+  }, [activeKey, children, defaultActiveKey, indexOfLastVisibleChild, moreTabText, handleDropdownTabClick]);
 
   return (
-    <div ref={containerElementRef}>
+    <div ref={setContainerElementRef}>
       <BaseTabs
         defaultActiveKey={defaultActiveKey}
         activeKey={activeKey}

src/hooks/tests/useIndexOfLastVisibleChild.test.jsx

@@ -12,12 +12,12 @@ window.ResizeObserver = window.ResizeObserver
   }));
 
 function TestComponent() {
-  const containerElementRef = React.useRef(null);
+  const [containerElementRef, setContainerElementRef] = React.useState(null);
   const overflowElementRef = React.useRef(null);
-  const indexOfLastVisibleChild = useIndexOfLastVisibleChild(containerElementRef.current, overflowElementRef.current);
+  const indexOfLastVisibleChild = useIndexOfLastVisibleChild(containerElementRef, overflowElementRef.current);
 
   return (
-    <div ref={containerElementRef} style={{ display: 'flex' }}>
+    <div ref={setContainerElementRef} style={{ display: 'flex' }}>
       <div style={{ width: '250px' }} className="element">Element 1</div>
       <div style={{ width: '250px' }} className="element">Element 2</div>
       <div style={{ width: '250px' }} className="element">Element 3</div>

src/hooks/useIndexOfLastVisibleChild.jsx

@@ -1,7 +1,5 @@
 import { useLayoutEffect, useState } from 'react';
 
-import useWindowSize from './useWindowSize';
-
 /**
  * This hook will find the index of the last child of a containing element
  * that fits within its bounding rectangle. This is done by summing the widths
@@ -10,48 +8,48 @@ import useWindowSize from './useWindowSize';
  * @param {Element} containerElementRef - container element
  * @param {Element} overflowElementRef - overflow element
  *
- * The hook returns an array containing:
- * [indexOfLastVisibleChild, containerElementRef, overflowElementRef]
- *
- * indexOfLastVisibleChild - the index of the last visible child
- * containerElementRef - a ref to be added to the containing html node
- * overflowElementRef - a ref to be added to an html node inside the container
- *    that is likely to be used to contain a "More" type dropdown or other
- *    mechanism to reveal hidden children. The width of this element is always
- *    included when determining which children will fit or not. Usage of this ref
- *    is optional.
+ * The hook returns the index of the last visible child.
  */
 const useIndexOfLastVisibleChild = (containerElementRef, overflowElementRef) => {
   const [indexOfLastVisibleChild, setIndexOfLastVisibleChild] = useState(-1);
-  const windowSize = useWindowSize();
 
   useLayoutEffect(() => {
-    if (!containerElementRef) {
-      return;
+    function updateLastVisibleChildIndex() {
+      // Get array of child nodes from NodeList form
+      const childNodesArr = Array.prototype.slice.call(containerElementRef.children);
+      const { nextIndexOfLastVisibleChild } = childNodesArr
+        // filter out the overflow element
+        .filter(childNode => childNode !== overflowElementRef)
+        // sum the widths to find the last visible element's index
+        .reduce((acc, childNode, index) => {
+          acc.sumWidth += childNode.getBoundingClientRect().width;
+          if (acc.sumWidth <= containerElementRef.getBoundingClientRect().width) {
+            acc.nextIndexOfLastVisibleChild = index;
+          }
+          return acc;
+        }, {
+          // Include the overflow element's width to begin with. Doing this means
+          // sometimes we'll show a dropdown with one item in it when it would fit,
+          // but allowing this case dramatically simplifies the calculations we need
+          // to do above.
+          sumWidth: overflowElementRef ? overflowElementRef.getBoundingClientRect().width : 0,
+          nextIndexOfLastVisibleChild: -1,
+        });
+
+      setIndexOfLastVisibleChild(nextIndexOfLastVisibleChild);
+    }
+
+    if (containerElementRef) {
+      updateLastVisibleChildIndex();
+
+      const resizeObserver = new ResizeObserver(() => updateLastVisibleChildIndex());
+      resizeObserver.observe(containerElementRef);
+
+      return () => resizeObserver.disconnect();
     }
-    // Get array of child nodes from NodeList form
-    const childNodesArr = Array.prototype.slice.call(containerElementRef.children);
-    const { nextIndexOfLastVisibleChild } = childNodesArr
-      // filter out the overflow element
-      .filter(childNode => childNode !== overflowElementRef)
-      // sum the widths to find the last visible element's index
-      .reduce((acc, childNode, index) => {
-        acc.sumWidth += childNode.getBoundingClientRect().width;
-        if (acc.sumWidth <= containerElementRef.getBoundingClientRect().width) {
-          acc.nextIndexOfLastVisibleChild = index;
-        }
-        return acc;
-      }, {
-        // Include the overflow element's width to begin with. Doing this means
-        // sometimes we'll show a dropdown with one item in it when it would fit,
-        // but allowing this case dramatically simplifies the calculations we need
-        // to do above.
-        sumWidth: overflowElementRef ? overflowElementRef.getBoundingClientRect().width : 0,
-        nextIndexOfLastVisibleChild: -1,
-      });
-
-    setIndexOfLastVisibleChild(nextIndexOfLastVisibleChild);
-  }, [windowSize, containerElementRef, overflowElementRef]);
+
+    return undefined;
+  }, [containerElementRef, overflowElementRef]);
 
   return indexOfLastVisibleChild;
 };

src/hooks/useIndexOfLastVisibleChild.mdx

@@ -25,10 +25,10 @@ of the children until they exceed the width of the container.
     pointerEvents: 'none',
     visibility: 'hidden',
   };
-  const containerElementRef = React.useRef(null);
+  const [containerElementRef, setContainerElementRef] = React.useState(null);
   const overflowElementRef = React.useRef(null);
   const indexOfLastVisibleChild = useIndexOfLastVisibleChild(
-    containerElementRef.current,
+    containerElementRef,
     overflowElementRef.current,
   );
   const elements = ['Element 1', 'Element 2', 'Element 3', 'Element 4', 'Element 5', 'Element 6', 'Element 7'];
@@ -71,7 +71,7 @@ of the children until they exceed the width of the container.
   }, [indexOfLastVisibleChild]);
 
   return (
-    <div className="d-flex" ref={containerElementRef}>
+    <div className="d-flex" ref={setContainerElementRef}>
       {children}
     </div>
   )