[reactjs] How to generate unique IDs for form labels in React?

I have form elements with labels and I want to have unique IDs to link labels to elements with htmlFor attribute. Something like this:

React.createClass({
    render() {
        const id = ???;
        return (
            <label htmlFor={id}>My label</label>
            <input id={id} type="text"/>
        );
    }
});

I used to generate IDs based on this._rootNodeID but it’s unavailable since React 0.13. What is the best and/or simplest way to do it now?

Don't use IDs at all if you don't need to, instead wrap the input in a label like this:

<label>
   My Label
   <input type="text"/>
</label>

Then you won't need to worry about unique IDs.

Hopefully this is helpful to anyone coming looking for a universal/isomorphic solution, since the checksum issue is what led me here in the first place.

As said above, I've created a simple utility to sequentially create a new id. Since the IDs keep incrementing on the server, and start over from 0 in the client, I decided to reset the increment each the SSR starts.

// utility to generate ids
let current = 0

export default function generateId (prefix) {
  return `${prefix || 'id'}-${current++}`
}

export function resetIdCounter () { current = 0 }

And then in the root component's constructor or componentWillMount, call the reset. This essentially resets the JS scope for the server in each server render. In the client it doesn't (and shouldn't) have any effect.

You could use a library such as node-uuid for this to make sure you get unique ids.

Install using:

npm install node-uuid --save

Then in your react component add the following:

import {default as UUID} from "node-uuid";
import {default as React} from "react";

export default class MyComponent extends React.Component {   
  componentWillMount() {
    this.id = UUID.v4();
  }, 
  render() {
    return (
      <div>
        <label htmlFor={this.id}>My label</label>
        <input id={this.id} type="text"/>
      </div>
    );
  }   
}

I create a uniqueId generator module (Typescript):

const uniqueId = ((): ((prefix: string) => string) => {
  let counter = 0;
  return (prefix: string): string => `${prefix}${++counter}`;
})();

export default uniqueId;

And use top module to generate unique ids:

import React, { FC, ReactElement } from 'react'
import uniqueId from '../../modules/uniqueId';

const Component: FC = (): ReactElement => {
  const [inputId] = useState(uniqueId('input-'));
  return (
    <label htmlFor={inputId}>
      <span>text</span>
      <input id={inputId} type="text" />
    </label>
  );
};     

For the usual usages of label and input, it's just easier to wrap input into a label like this:

import React from 'react'

const Field = props => (
  <label>
    <span>{props.label}</span>
    <input type="text"/>
  </label>
)      

It's also makes it possible in checkboxes/radiobuttons to apply padding to root element and still getting feedback of click on input.

I found an easy solution like this:

class ToggleSwitch extends Component {
  static id;

  constructor(props) {
    super(props);

    if (typeof ToggleSwitch.id === 'undefined') {
      ToggleSwitch.id = 0;
    } else {
      ToggleSwitch.id += 1;
    }
    this.id = ToggleSwitch.id;
  }

  render() {
    return (
        <input id={`prefix-${this.id}`} />
    );
  }
}

Following up as of 2019-04-04, this seems to be able to be accomplished with the React Hooks' useState:

import React, { useState } from 'react'
import uniqueId from 'lodash/utility/uniqueId'

const Field = props => {
  const [ id ] = useState(uniqueId('myprefix-'))

  return (
    <div>
      <label htmlFor={id}>{props.label}</label>
      <input id={id} type="text"/>
    </div>
  )      
}

export default Field

As I understand it, you ignore the second array item in the array destructuring that would allow you to update id, and now you've got a value that won't be updated again for the life of the component.

The value of id will be myprefix-<n> where <n> is an incremental integer value returned from uniqueId. If that's not unique enough for you, consider making your own like

function gen4() {
  return Math.random().toString(16).slice(-4)
}

function simpleUniqueId(prefix) {
  return (prefix || '').concat([
    gen4(),
    gen4(),
    gen4(),
    gen4(),
    gen4(),
    gen4(),
    gen4(),
    gen4()
  ].join(''))
}

or check out the library I published with this here: https://github.com/rpearce/simple-uniqueid. There are also hundreds or thousands of other unique ID things out there, but lodash's uniqueId with a prefix should be enough to get the job done.

Update 2019-07-10

Thanks to @Huong Hk for pointing me to hooks lazy initial state, the sum of which is that you can pass a function to useState that will only be run on the initial mount.

// before
const [ id ] = useState(uniqueId('myprefix-'))

// after
const [ id ] = useState(() => uniqueId('myprefix-'))

The id should be placed inside of componentWillMount (update for 2018) constructor, not render. Putting it in render will re-generate new ids unnecessarily.

If you're using underscore or lodash, there is a uniqueId function, so your resulting code should be something like:

constructor(props) {
    super(props);
    this.id = _.uniqueId("prefix-");
}

render() { 
  const id = this.id;
  return (
    <div>
        <input id={id} type="checkbox" />
        <label htmlFor={id}>label</label>
    </div>
  );
}

2019 Hooks update:

import React, { useState } from 'react';
import _uniqueId from 'lodash/uniqueId';

const MyComponent = (props) => {
  // id will be set once when the component initially renders, but never again
  // (unless you assigned and called the second argument of the tuple)
  const [id] = useState(_uniqueId('prefix-'));
  return (
    <div>
      <input id={id} type="checkbox" />
      <label htmlFor={id}>label</label>
    </div>
  );
}