[Solved]-How can I use multiple refs for an array of elements with hooks?-Reactjs

We can't use state because we need the ref to be available before the render method is called. We can't call useRef an arbitrary number of times, but we can call it once:

Assuming arr is a prop with the array of things:

const refs = useRef([]);
// free any refs that we're not using anymore
refs.current = refs.current.slice(0, arr.length);
// initialize any new refs
for (let step = refs.current.length; step < arr.length; step++) {
    refs.current[step] = createRef();
}

import React, { useRef } from "react";

export default function App() {
  const arr = [1, 2, 3];

  const refs = useRef([]);

  return (
    <div className="App">
      {arr.map((item, index) => {
        return (
          <div
            key={index}
            ref={(element) => {
              refs.current[index] = element;
            }}
          >
            {item}
          </div>
        );
      })}
    </div>
  );
}

Credits: https://eliaslog.pw/how-to-add-multiple-refs-to-one-useref-hook/

You can use a father element to get a bounch of children elements.

In my case i was trying to get a bounch of inputs inside my form element then i get the form element and use it to handle with all the inputs.

Somthing like that:

function Foo() {
    const fields = useRef<HTMLFormElement>(null);

    function handlePopUp(e) {
      e.preventDefault();
    
      Array.from(fields.current)
        .forEach((input: HTMLInputElement | HTMLTextAreaElement) => {
          input.value = '';
        });
    }

    return (
    <form onSubmit={(e) => handlePopUp(e)} ref={fields}>

      <input
        placeholder="Nome"
        required
        id="name"
        type="text"
        name="name"
      />
      <input
        placeholder="E-mail"
        required
        id="email"
        type="email"
        name="email"
      />
      <input
        placeholder="Assunto"
        required
        id="subject"
        type="text"
        name="subject"
      />
      <textarea
        cols={120}
        placeholder="Descrição"
        required
        id="description"
        name="description"
      />

      <button type="submit" disabled={state.submitting}>enviar</button>
    </form>  
    );
}

React will re-render an element when its ref changes (referential equality / "triple-equals" check).

Most answers here do not take this into account. Even worse: when the parent renders and re-initializes the ref objects, all children will re-render, even if they are memoized components (React.PureComponent or React.memo)!

The solution below has no unnecessary re-renders, works with dynamic lists and does not even introduce an actual side effect. Accessing an undefined ref is not possible. A ref is initialized upon the first read. After that, it remains referentially stable.

const useGetRef = () => {
  const refs = React.useRef({})
  return React.useCallback(
    (idx) => (refs.current[idx] ??= React.createRef()),
    [refs]
  )
}

const Foo = ({ items }) => {
  const getRef = useGetRef()
  return items.map((item, i) => (
    <div ref={getRef(i)} key={item.id}>
      {/* alternatively, to access refs by id: `getRef(item.id)` */}
      {item.title}
    </div>
  ))
}

Caveat: When items shrinks over time, unused ref objects will not be cleaned up. When React unmounts an element, it will correctly set ref[i].current = null, but the "empty" refs will remain.

You can avoid the complexity array refs bring in combination with useEffect by moving the children into a separate component. This has other advantages the main one being readability and making it easier to maintain.

const { useRef, useState, useEffect } = React;

const ListComponent = ({ el }) => {
  const elRef = useRef();
  const [elWidth, setElWidth] = useState();

  useEffect(() => {
    setElWidth(elRef.current.offsetWidth);
  }, []);

  return (
    <div ref={elRef} style={{ width: `${el * 100}px` }}>
      Width is: {elWidth}
    </div>
  );
};

const App = () => {

  return (
    <div>
      {[1, 2, 3].map((el, i) => (
        <ListComponent key={i} el={el} />
      ))}
    </div>
  );
};

ReactDOM.render(<App />, document.getElementById('root'));

If I understand correctly, useEffect should only be used for side effects, for this reason I chose instead to use useMemo.

const App = props => {
    const itemsRef = useMemo(() => Array(props.items.length).fill().map(() => createRef()), [props.items]);

    return props.items.map((item, i) => (
        <div 
            key={i} 
            ref={itemsRef[i]} 
            style={{ width: `${(i + 1) * 100}px` }}>
        ...
        </div>
    ));
};

Then if you want to manipulate the items / use side effects you can do something like:

useEffect(() => {
    itemsRef.map(e => e.current).forEach((e, i) => { ... });
}, [itemsRef.length])

I use the useRef hook to create panels of data that I want to control independently. First I initialize the useRef to store an array:

import React, { useRef } from "react";

const arr = [1, 2, 3];

const refs = useRef([])

When initializing the array we observe that it actually looks like this:

//refs = {current: []}

Then we apply the map function to create the panels using the div tag which we will be referencing, adds the current element to our refs.current array with one button to review:

arr.map((item, index) => {
  <div key={index} ref={(element) => {refs.current[index] = element}}>
    {item}
    <a
      href="#"
      onClick={(e) => {
        e.preventDefault();
        onClick(index)
      }}
    >
      Review
    </a>
})

Finally a function that receives the index of the pressed button we can control the panel that we want to show

const onClick = (index) => {
  console.log(index)
  console.log(refs.current[index])
}

Finally the complete code would be like this

import React, { useRef } from "react";

const arr = [1, 2, 3];

const refs = useRef([])
//refs = {current: []}

const onClick = (index) => {
  console.log(index)
  console.log(refs.current[index])
}

const MyPage = () => {
   const content = arr.map((item, index) => {
     <div key={index} ref={(element) => {refs.current[index] = element}}>
       {item}
       <a
         href="#"
         onClick={(e) => {
           e.preventDefault();
           onClick(index)
         }}
       >
         Review
       </a>
   })
   return content
}

export default MyPage

It works for me! Hoping that this knowledge will be of use to you.

You can use an array(or an object) to keep track of all the refs and use a method to add ref to the array.

NOTE: If you are adding and removing refs you would have to empty the array every render cycle.

import React, { useRef } from "react";

const MyComponent = () => {
   // intialize as en empty array
   const refs = useRefs([]); // or an {}
   // Make it empty at every render cycle as we will get the full list of it at the end of the render cycle
   refs.current = []; // or an {}

   // since it is an array we need to method to add the refs
   const addToRefs = el => {
     if (el && !refs.current.includes(el)) {
       refs.current.push(el);
     }
    };
    return (
     <div className="App">
       {[1,2,3,4].map(val => (
         <div key={val} ref={addToRefs}>
           {val}
         </div>
       ))}
     </div>
   );

}

working example https://codesandbox.io/s/serene-hermann-kqpsu

Note that you shouldn't use useRef in a loop for a simple reason: the order of used hooks does matter!

The documentation says

Don’t call Hooks inside loops, conditions, or nested functions. Instead, always use Hooks at the top level of your React function. By following this rule, you ensure that Hooks are called in the same order each time a component renders. That’s what allows React to correctly preserve the state of Hooks between multiple useState and useEffect calls. (If you’re curious, we’ll explain this in depth below.)

But consider that it obviously applies to dynamic arrays... but if you're using static arrays (you ALWAYS render the same amount of components) don't worry too much about that, be aware of what you're doing and leverage it 😉

Assuming that your array contains non primitives, you could use a WeakMap as the value of the Ref.

function MyComp(props) {
    const itemsRef = React.useRef(new WeakMap())

    // access an item's ref using itemsRef.get(someItem)

    render (
        <ul>
            {props.items.map(item => (
                <li ref={el => itemsRef.current.set(item, el)}>
                    {item.label}
                </li>
            )}
        </ul>
    )
}

The simplest and most effective way is to not use useRef at all. Just use a callback ref that creates a new array of refs on every render.

function useArrayRef() {
  const refs = []
  return [refs, el => el && refs.push(el)]
}

Demo

<div id="root"></div>

<script type="text/babel" defer>
const { useEffect, useState } = React

function useArrayRef() {
  const refs = []
  return [refs, el => el && refs.push(el)]
}

const App = () => {
  const [elements, ref] = useArrayRef()
  const [third, setThird] = useState(false)
  
  useEffect(() => {
    console.log(elements)
  }, [third])

  return (
    <div>
      <div ref={ref}>
        <button ref={ref} onClick={() => setThird(!third)}>toggle third div</button>
      </div>
      <div ref={ref}>another div</div>
      { third && <div ref={ref}>third div</div>}
    </div>
  );
}

ReactDOM.render(<App />, document.getElementById("root"));
</script>

<script src="https://unpkg.com/@babel/standalone@7/babel.min.js"></script>
<script src="https://unpkg.com/react@17/umd/react.production.min.js"></script>
<script src="https://unpkg.com/react-dom@17/umd/react-dom.production.min.js"></script>

There are two ways

1. use one ref with multiple current elements

const inputRef = useRef([]);

inputRef.current[idx].focus();

<input
  ref={el => inputRef.current[idx] = el}
/>

const {useRef} = React;
const App = () => {
  const list = [...Array(8).keys()];
  const inputRef = useRef([]);
  const handler = idx => e => {
    const next = inputRef.current[idx + 1];
    if (next) {
      next.focus()
    }
  };
  return (
    <div className="App">
      <div className="input_boxes">
        {list.map(x => (
        <div>
          <input
            key={x}
            ref={el => inputRef.current[x] = el} 
            onChange={handler(x)}
            type="number"
            className="otp_box"
          />
        </div>
        ))}
      </div>
    </div>
  );
}
ReactDOM.render(<App />, document.getElementById("root"));

<div id="root"></div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.12.0/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.12.0/umd/react-dom.production.min.js"></script>

2. use an Array of ref

   As the above post said, it's not recommended since the official guideline (and the inner lint check) won't allow it to pass.

   Don’t call Hooks inside loops, conditions, or nested functions. Instead, always use Hooks at the top level of your React function. By following this rule, you ensure that Hooks are called in the same order each time a component renders.

   However, since it's not our current case, the demo below still works, only not recommended.

const inputRef = list.map(x => useRef(null));

inputRef[idx].current.focus();

<input
  ref={inputRef[idx]}
/>

const {useRef} = React;
const App = () => {
const list = [...Array(8).keys()];
const inputRef = list.map(x => useRef(null));
const handler = idx => () => {
  const next = inputRef[idx + 1];
  if (next) {
    next.current.focus();
  }
};
return (
  <div className="App">
    <div className="input_boxes">
      {list.map(x => (
      <div>
        <input
          key={x}
          ref={inputRef[x]}
          onChange={handler(x)}
          type="number"
          className="otp_box"
        />
      </div>
      ))}
    </div>
  </div>
);
}
ReactDOM.render(<App />, document.getElementById("root"));

<div id="root"></div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.12.0/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.12.0/umd/react-dom.production.min.js"></script>

As you cannot use hooks inside loops, here is a solution in order to make it work when the array changes over the time.

I suppose the array comes from the props :

const App = props => {
    const itemsRef = useRef([]);
    // you can access the elements with itemsRef.current[n]

    useEffect(() => {
       itemsRef.current = itemsRef.current.slice(0, props.items.length);
    }, [props.items]);

    return props.items.map((item, i) => (
      <div 
          key={i} 
          ref={el => itemsRef.current[i] = el} 
          style={{ width: `${(i + 1) * 100}px` }}>
        ...
      </div>
    ));
}