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

How do I select certain bars in react.js?

This is my code:

var Progressbar = React.createClass({
    getInitialState: function () {
        return { completed: this.props.completed };
    },
    addPrecent: function (value) {
        this.props.completed += value;
        this.setState({ completed: this.props.completed });
    },

    render: function () {

        var completed = this.props.completed;
        if (completed < 0) { completed = 0 };


        return (...);
    }

I want to use this React component:

var App = React.createClass({
    getInitialState: function () {

        return { baction: 'Progress1' };
    },
    handleChange: function (e) {
        var value = e.target.value;
        console.log(value);
        this.setState({ baction: value });
    },
    handleClick10: function (e) {
        console.log('You clicked: ', this.state.baction);
        document.getElementById(this.state.baction).addPrecent(10);
    },
    render: function () {
        return (
            <div class="center">Progress Bars Demo
            <Progressbar completed={25} id="Progress1" />
                <h2 class="center"></h2>
                <Progressbar completed={50} id="Progress2" />
                <h2 class="center"></h2>
                <Progressbar completed={75} id="Progress3" />
                <h2 class="center"></h2>
                <span>
                    <select name='selectbar' id='selectbar' value={this.state.baction} onChange={this.handleChange}>
                        <option value="Progress1">#Progress1</option>
                        <option value="Progress2">#Progress2</option>
                        <option value="Progress3">#Progress3</option>
                    </select>
                    <input type="button" onClick={this.handleClick10} value="+10" />
                    <button>+25</button>
                    <button>-10</button>
                    <button>-25</button>
                </span>
            </div>
        )
    }
});

I want to execute the handleClick10 function and perform the operation for my selected progressbar. But the result I get is:

 You clicked:  Progress1
 TypeError: document.getElementById(...) is null

How do I select the certain Element in react.js?

You can replace

document.getElementById(this.state.baction).addPrecent(10);

with

this.refs[this.state.baction].addPrecent(10);


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

Disclaimer: While the top answer is probably a better solution, as a beginner it's a lot to take in when all you want is something very simple. This is intended as a more direct answer to your original question "How can I select certain elements in React"

I think the confusion in your question is because you have React components which you are being passed the id "Progress1", "Progress2" etc. I believe this is not setting the html attribute 'id', but the React component property. e.g.

class ProgressBar extends React.Component {
    constructor(props) {
        super(props)
        this.state = {
            id: this.props.id    <--- ID set from <ProgressBar id="Progress1"/>
        }
    }        
}

As mentioned in some of the answers above you absolutely can use document.querySelector inside of your React app, but you have to be clear that it is selecting the html output of your components' render methods. So assuming your render output looks like this:

render () {
    const id = this.state.id
    return (<div id={"progress-bar-" + id}></div>)
}

Then you can elsewhere do a normal javascript querySelector call like this:

let element = document.querySelector('#progress-bar-Progress1')

put it your input field

ref={(el) => this.myInput = el}

For getting the element in react you need to use ref and inside the function you can use the ReactDOM.findDOMNode method.

But what I like to do more is to call the ref right inside the event

<input type="text" ref={ref => this.myTextInput = ref} />

This is some good link to help you figure out.

Since React uses JSX code to create an HTML we cannot refer dom using regulation methods like documment.querySelector or getElementById.

Instead we can use React ref system to access and manipulate Dom as shown in below example:

constructor(props){

    super(props);
    this.imageRef = React.createRef(); // create react ref
}

componentDidMount(){

    **console.log(this.imageRef)** // acessing the attributes of img tag when dom loads
}


render = (props) => {

const {urls,description} = this.props.image;
    return (

            <img
             **ref = {this.imageRef} // assign the ref of img tag here**
             src = {urls.regular} 
             alt = {description}
             />

        );

}

}