How to add “refs” dynamically with react hooks?

Question

So I have an array of data in and I am generating a list of components with that data. I\'d like to have a ref on each generated element to calculate the height. I know how

Answer 1

I created a tiny npm package that exposes a React Hook to handle setting and getting refs dynamically as I often run into the same problem.

npm i use-dynamic-refs

Here's a simple example.

import React, { useEffect } from 'react';
import useDynamicRefs from 'use-dynamic-refs';

const Example = () =>  {
  const foo = ['random_id_1', 'random_id_2'];
  const [getRef, setRef] =  useDynamicRefs();

  useEffect(() => {
    // Get ref for specific ID 
    const id = getRef('random_id_1');
    console.log(id)
  }, [])

    return ( 
      <>
        {/* Simple set ref. */}
        <span ref={setRef('random_id_3')}></span>

         {/*  Set refs dynamically in Array.map() */}
        { foo.map( eachId => (
          <div key={eachId} ref={setRef(eachId)}>Hello {eachId}</div>))}
      </>
    )
}

export default Example;

Answer 2

You have to use a separate set of hooks for each item, and this means you have to define a component for the items (or else you’re using hooks inside a loop, which isn’t allowed).

const Item = ({ text }) => {
    const ref = useRef()
    const [ height, setHeight ] = useState()
    useLayoutEffect(() => {
        setHeight( ref.current.getBoundingClientRect().height )
    }, [])
    return <div ref={ref}>{text}</div>
}

Answer 3

Not sure i fully understand your intent, but i think you want something like this:

const {
  useState,
  useRef,
  createRef,
  useEffect
} = React;

const data = [
  {
    text: "test1"
  },
  {
    text: "test2"
  }
];

const Component = () => {
  const [heights, setHeights] = useState([]);
  const elementsRef = useRef(data.map(() => createRef()));

  useEffect(() => {
    const nextHeights = elementsRef.current.map(
      ref => ref.current.getBoundingClientRect().height
    );
    setHeights(nextHeights);
  }, []);

  return (
    <div>
      {data.map((item, index) => (
        <div ref={elementsRef.current[index]} key={index} className={`item item-${index}`}>
          {`${item.text} - height(${heights[index]})`}
        </div>
      ))}
    </div>
  );
};

const rootElement = document.getElementById("root");
ReactDOM.render(<Component />, rootElement);

.item {
  box-sizing: border-box;
  display: flex;
  align-items: center;
  justify-content: center;
  border: 1px solid #ccc;
}

.item-0 {
  height: 25px;
}

.item-1 {
  height: 50px;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.8.6/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.8.6/umd/react-dom.production.min.js"></script>
<div id="root"/>