ReactJS - Get Height of an element

How can I get the Height of an element after React renders that element?

HTML

<div id="container">
<!-- This element's contents will be replaced with your component. -->
<p>
jnknwqkjnkj<br>
jhiwhiw (this is 36px height)
</p>
</div>

ReactJS

var DivSize = React.createClass({

  render: function() {
    let elHeight = document.getElementById('container').clientHeight
    return <div className="test">Size: <b>{elHeight}px</b> but it should be 18px after the render</div>;
  }
});

ReactDOM.render(
  <DivSize />,
  document.getElementById('container')
);

RESULT

Size: 36px but it should be 18px after the render

It's calculating the container height before the render (36px). I want to get the height after the render. The right result should be 18px in this case. jsfiddle

Following is an up to date ES6 example using a ref.

Remember that we have to use a React class component since we need to access the Lifecycle method componentDidMount() because we can only determine the height of an element after it is rendered in the DOM.

import React, {Component} from 'react'
import {render} from 'react-dom'

class DivSize extends Component {

  constructor(props) {
    super(props)

    this.state = {
      height: 0
    }
  }

  componentDidMount() {
    const height = this.divElement.clientHeight;
    this.setState({ height });
  }

  render() {
    return (
      <div 
        className="test"
        ref={ (divElement) => { this.divElement = divElement } }
      >
        Size: <b>{this.state.height}px</b> but it should be 18px after the render
      </div>
    )
  }
}

render(<DivSize />, document.querySelector('#container'))

You can find the running example here: https://codepen.io/bassgang/pen/povzjKw

For those who are interested in using react hooks, this might help you get started.

import React, { useState, useEffect, useRef } from 'react'

export default () => {
  const [height, setHeight] = useState(0)
  const ref = useRef(null)

  useEffect(() => {
    setHeight(ref.current.clientHeight)
  })

  return (
    <div ref={ref}>
      {height}
    </div>
  )
}

See this fiddle (actually updated your's)

You need to hook into componentDidMount which is run after render method. There, you get actual height of element.

var DivSize = React.createClass({
    getInitialState() {
    return { state: 0 };
  },

  componentDidMount() {
    const height = document.getElementById('container').clientHeight;
    this.setState({ height });
  },

  render: function() {
    return (
        <div className="test">
        Size: <b>{this.state.height}px</b> but it should be 18px after the render
      </div>
    );
  }
});

ReactDOM.render(
  <DivSize />,
  document.getElementById('container')
);

<script src="https://facebook.github.io/react/js/jsfiddle-integration-babel.js"></script>

<div id="container">
<p>
jnknwqkjnkj<br>
jhiwhiw (this is 36px height)
</p>
    <!-- This element's contents will be replaced with your component. -->
</div>

Instead of using document.getElementById(...), a better (up to date) solution is to use the React useRef hook that stores a reference to the component/element, combined with a useEffect hook, which fires at component renders.

import React, {useState, useEffect, useRef} from 'react';

export default App = () => {
  const [height, setHeight] = useState(0);
  const elementRef = useRef(null);

  useEffect(() => {
    setHeight(elementRef.current.clientHeight);
  }, []); //empty dependency array so it only runs once at render

  return (
    <div ref={elementRef}>
      {height}
    </div>
  )
}

ReactJS - Get Height of an element

Related

Recent Posts