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

HTML

jnknwqkjnkj
jhiwhiw (this is 36px height)

ReactJS

var DivSize = React.createClass({

  render: function() {
    let elHeight = document.getElementById('container').clientHeight
    return 
Size: {elHeight}px but it should be 18px after the render
; } }); ReactDOM.render( , 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

faia20

Ответов: 15

Ответы (15)

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 (
        
Size: {this.state.height}px but it should be 18px after the render
); } }); ReactDOM.render( , document.getElementById('container') );


jnknwqkjnkj
jhiwhiw (this is 36px height)

I found useful npm package https://www.npmjs.com/package/element-resize-detector

An optimized cross-browser resize listener for elements.

Can use it with React component or functional component(Specially useful for react hooks)

An alternative solution, in case you want to retrieve the size of a React element synchronously without having to visibly render the element, you can use ReactDOMServer and DOMParser.

I use this function to get the height of a my list item renderer when using react-window (react-virtualized) instead of having to hardcode the required itemSize prop for a FixedSizeList.

utilities.js:

/**
 * @description Common and reusable functions 
 * 
 * @requires react-dom/server
 * 
 * @public
 * @module
 * 
 */
import ReactDOMServer from "react-dom/server";

/**
 * @description Retrieve the width and/or heigh of a React element without rendering and committing the element to the DOM.
 * 
 * @param {object} elementJSX - The target React element written in JSX.
 * @return {object} 
 * @public
 * @function
 * 
 * @example
 * 
 * const { width, height } = getReactElementSize( 
); * console.log(`W: ${width}, H: ${height}); // W: 20, H: 40 * */ const getReactElementSize = (elementJSX) => { const elementString = ReactDOMServer.renderToStaticMarkup(elementJSX); const elementDocument = new DOMParser().parseFromString(elementString, "text/html"); const elementNode = elementDocument.getRootNode().body.firstChild; const container = document.createElement("div"); const containerStyle = { display: "block", position: "absolute", boxSizing: "border-box", margin: "0", padding: "0", visibility: "hidden" }; Object.assign(container.style, containerStyle); container.appendChild(elementNode); document.body.appendChild(container); const width = container.clientWidth; const height = container.clientHeight; container.removeChild(elementNode); document.body.removeChild(container); return { width, height }; }; /** * Export module * */ export { getReactElementSize };

My 2020's (or 2019) answer

import React, {Component, useRef, useLayoutEffect} from 'react';
import { useDispatch } from 'react-redux';
import { Toast, ToastBody, ToastHeader } from 'reactstrap';

import {WidgetHead} from './WidgetHead';

export const Widget = ({title, toggle, reload, children, width, name}) => {
    let myself = useRef(null);
    const dispatch = useDispatch();
    useLayoutEffect(()=>{
        if (myself.current) {
            const height = myself.current.clientHeight
            dispatch({type:'GRID_WIDGET_HEIGHT', widget:name, height})
        }
    }, [myself.current, myself.current?myself.current.clientHeight:0])

    return (
        
            
            
            {children}
            
        
    )
}

let use your imagination for what is missing here (WidgetHead), reactstrap is something you can find on npm: replace innerRef with ref for a legacy dom element (say a

).

useEffect or useLayoutEffect

The last is said to be synchronous for changes

useLayoutEffect (or useEffect) second argument

Second argument is an array, and it is checked before executing the function in the first argument.

I used

[myself.current, myself.current?myself.current.clientHeight:0]

because myself.current is null before rendering, and that is a good thing not to check, the second parameter at the end myself.current.clientHeight is what I want to check for changes.

what I am solving here (or trying to solve)

I am solving here the problem of widget on a grid that change its height by their own will, and the grid system should be elastic enough to react ( https://github.com/STRML/react-grid-layout ).

you can also use getBoundingClientRect() to get height, width.

const [width, setWidth] = useState(0);

useEffect(() => {
    const element = document.getElementById('element-id');
    if (element) {
      setWidth(element.getBoundingClientRect().width); // or height
    }
  }, []);

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 (
    
{height}
) }

Here's a nice reusable hook amended from https://swizec.com/blog/usedimensions-a-react-hook-to-measure-dom-nodes:

import { useState, useCallback, useEffect } from 'react';

function getDimensionObject(node) {
  const rect = node.getBoundingClientRect();

  return {
    width: rect.width,
    height: rect.height,
    top: 'x' in rect ? rect.x : rect.top,
    left: 'y' in rect ? rect.y : rect.left,
    x: 'x' in rect ? rect.x : rect.left,
    y: 'y' in rect ? rect.y : rect.top,
    right: rect.right,
    bottom: rect.bottom
  };
}

export function useDimensions(data = null, liveMeasure = true) {
  const [dimensions, setDimensions] = useState({});
  const [node, setNode] = useState(null);

  const ref = useCallback(node => {
    setNode(node);
  }, []);

  useEffect(() => {
    if (node) {
      const measure = () =>
        window.requestAnimationFrame(() =>
          setDimensions(getDimensionObject(node))
        );
      measure();

      if (liveMeasure) {
        window.addEventListener('resize', measure);
        window.addEventListener('scroll', measure);

        return () => {
          window.removeEventListener('resize', measure);
          window.removeEventListener('scroll', measure);
        };
      }
    }
  }, [node, data]);

  return [ref, dimensions, node];
}

To implement:

import { useDimensions } from '../hooks';

// Include data if you want updated dimensions based on a change.
const MyComponent = ({ data }) => {
  const [
    ref,
    { height, width, top, left, x, y, right, bottom }
  ] = useDimensions(data);

  console.log({ height, width, top, left, x, y, right, bottom });

  return (
    
{data.map(d => (

{d.title}

))}
); };

I found the other answers with React hooks were not updating properly upon resize.

After searching around I found this blog post that gives a working React hook that observes resize events:

The TL;DR is here:

npm install --save resize-observer-polyfill

// useResizeObserver.js
import { useEffect, useRef } from 'react';
import PropTypes from 'prop-types';
import ResizeObserver from 'resize-observer-polyfill';

const useObserver = ({ callback, element }) => {

  const current = element && element.current;

  const observer = useRef(null);

  useEffect(() => {
      // if we are already observing old element
      if (observer && observer.current && current) {
        observer.current.unobserve(current);
      }
      const resizeObserverOrPolyfill =  ResizeObserver;
      observer.current = new resizeObserverOrPolyfill(callback);
      observe();

      return () => {
        if (observer && observer.current && element &&
           element.current) {
          observer.current.unobserve(element.current);
        }
      };
  }, [current]);

  const observe = () => {
    if (element && element.current && observer.current) {
      observer.current.observe(element.current);
    }
  };

};

useObserver.propTypes = {
  element: PropTypes.object,
  callback: PropTypes.func,
};

export default useObserver;

Then an example usage in a component:

// shape.js
import React, { useEffect, useState, useRef } from 'react';
import useResizeObserver from 'path/to/useResizeObserver.js';

const Shape = () => {
  const [height, setHeight] = useState(0);
  const svgRef = useRef(null);

  const doHeightAdjustment = () => {
    setHeight(svgRef.current.clientHeight);
  };

  useResizeObserver({callback: doHeightAdjustment, element: svgRef});

  return (
    
{height}
); }; export default Shape;

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 (
    
{height}
) }

Use the useMeasure as custom hook (Typescript, SSR, hook):

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

interface ContainerSize {
  width: number;
  height: number;
}

type UseMeasureArgs = () => {
  ref: React.RefObject;
  size: ContainerSize;
  windowSize: ContainerSize;
};

const initSize: ContainerSize = { width: 0, height: 0 };

const useMeasure: UseMeasureArgs = () => {
  const ref = useRef(null);
  const [size, setSize] = useState(initSize);
  const [windowSize, setWindowSize] = useState(initSize);

  useEffect(() => {
    if (ref.current) {
      setSize({ width: ref.current.offsetWidth, height: ref.current.offsetHeight });
    }
    if (typeof window !== 'undefined') {
      setWindowSize({
        width: window.innerWidth,
        height: window.innerHeight,
      });
    }
  }, []);

  return { ref, size, windowSize };
};

export default useMeasure;

it might show zero. setTimeout helps to get the correct value and update the state.

import React, { useState, useEffect, useRef } from 'react'
    
    export default () => {
      const [height, setHeight] = useState(0)
      const ref= useRef(null)
    
      useEffect(() => {
       if(elemRef.current.clientHeight){
         setTimeout(() => {
           setHeight(ref.current.clientHeight) 
         }, 1000)
       }
      })
    
      return (
        
{height}
) }

Here is another one if you need window resize event:

class DivSize extends React.Component {

  constructor(props) {
    super(props)

    this.state = {
      width: 0,
      height: 0
    }
    this.resizeHandler = this.resizeHandler.bind(this);
  }

  resizeHandler() {
    const width = this.divElement.clientWidth;
    const height = this.divElement.clientHeight;
    this.setState({ width, height });
  }

  componentDidMount() {
    this.resizeHandler();
    window.addEventListener('resize', this.resizeHandler);
  }

  componentWillUnmount(){
    window.removeEventListener('resize', this.resizeHandler);
  }

  render() {
    return (
      
{ this.divElement = divElement } } > Size: widht: {this.state.width}px, height: {this.state.height}px
) } } ReactDOM.render(, document.querySelector('#container'))

code pen

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 (
      
{ this.divElement = divElement } } > Size: {this.state.height}px but it should be 18px after the render
) } } render(, document.querySelector('#container'))

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

You would also want to use refs on the element instead of using document.getElementById, it's just a slightly more robust thing.

Using with hooks :

This answer would be helpful if your content dimension changes after loading.

onreadystatechange : Occurs when the load state of the data that belongs to an element or a HTML document changes. The onreadystatechange event is fired on a HTML document when the load state of the page's content has changed.

import {useState, useEffect, useRef} from 'react';
const ref = useRef();
useEffect(() => {
    document.onreadystatechange = () => {
      console.log(ref.current.clientHeight);
    };
  }, []);

I was trying to work with a youtube video player embedding whose dimensions may change after loading.

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