[javascript] How to access a DOM element in React? What is the equilvalent of document.getElementById() in React

You can do that by specifying the ref

EDIT: In react v16.8.0 with function component, you can define a ref with useRef. Note that when you specify a ref on a function component, you need to use React.forwardRef on it to forward the ref to the DOM element of use useImperativeHandle to to expose certain functions from within the function component

Ex:

const Child1 = React.forwardRef((props, ref) => {
    return <div ref={ref}>Child1</div> 
});

const Child2 = React.forwardRef((props, ref) => {
    const handleClick= () =>{};
    useImperativeHandle(ref,() => ({
       handleClick
    }))
    return <div>Child2</div> 
});
const App = () => {
    const child1 = useRef(null);
    const child2 = useRef(null);

    return (
        <>
           <Child1 ref={child1} />
           <Child1 ref={child1} />
        </>
    )
}

EDIT:

In React 16.3+, use React.createRef() to create your ref:

class MyComponent extends React.Component {
  constructor(props) {
    super(props);
    this.myRef = React.createRef();
  }
  render() {
    return <div ref={this.myRef} />;
  }
}

In order to access the element, use:

const node = this.myRef.current;

DOC for using React.createRef()

EDIT

However facebook advises against it because string refs have some issues, are considered legacy, and are likely to be removed in one of the future releases.

From the docs:

Legacy API: String Refs

If you worked with React before, you might be familiar with an older API where the ref attribute is a string, like "textInput", and the DOM node is accessed as this.refs.textInput. We advise against it because string refs have some issues, are considered legacy, and are likely to be removed in one of the future releases. If you're currently using this.refs.textInput to access refs, we recommend the callback pattern instead.

A recommended way for React 16.2 and earlier is to use the callback pattern:

<Progressbar completed={25} id="Progress1" ref={(input) => {this.Progress[0] = input }}/>

<h2 class="center"></h2>

<Progressbar completed={50} id="Progress2" ref={(input) => {this.Progress[1] = input }}/>

  <h2 class="center"></h2>

<Progressbar completed={75} id="Progress3" ref={(input) => {this.Progress[2] = input }}/>

DOC for using callback

Even older versions of react defined refs using string like below

<Progressbar completed={25} id="Progress1" ref="Progress1"/>

    <h2 class="center"></h2>

    <Progressbar completed={50} id="Progress2" ref="Progress2"/>

      <h2 class="center"></h2>

    <Progressbar completed={75} id="Progress3" ref="Progress3"/>

In order to get the element just do

var object = this.refs.Progress1;

Remember to use this inside an arrow function block like:

print = () => {
  var object = this.refs.Progress1;  
}

and so on...