React usePrevious Hook

By  on  

Hooks are essential for the functional component pattern in React. One frequent logic comparison with class components was comparing a previous prop value with a current prop value via lifecycle methods. So what's an easy pattern for duplicating previous value comparisons in functional components?

The useRef and useEffect hooks allow us manage that same functionality in functional components via a custom hook -- usePrevious:

import { useEffect, useRef } from 'react';

export function usePrevious(value) {
  const ref = useRef();
  useEffect(() => {
    ref.current = value;
  }, [value]);
  return ref.current;
}

// Usage
export function MyComponent(props) {
  const { name } = props;
  const previousName = usePrevious(name);

  if(name != previousName) {
    // Do something
  }
}

I love this usePrevious hook, if only because I frequently forget to use the .current property and it helps avoid some boilerplate code. What are your thoughts on this pattern? Do you have any custom hooks you rely on?

Recent Features

  • By
    CSS @supports

    Feature detection via JavaScript is a client side best practice and for all the right reasons, but unfortunately that same functionality hasn't been available within CSS.  What we end up doing is repeating the same properties multiple times with each browser prefix.  Yuck.  Another thing we...

  • By
    5 More HTML5 APIs You Didn’t Know Existed

    The HTML5 revolution has provided us some awesome JavaScript and HTML APIs.  Some are APIs we knew we've needed for years, others are cutting edge mobile and desktop helpers.  Regardless of API strength or purpose, anything to help us better do our job is a...

Incredible Demos

  • By
    Page Visibility API

    One event that's always been lacking within the document is a signal for when the user is looking at a given tab, or another tab. When does the user switch off our site to look at something else? When do they come back?

  • By
    Create a Simple Dojo Accordion

    Let's be honest:  even though we all giggle about how cheap of a thrill JavaScript accordions have become on the web, they remain an effective, useful widget.  Lots of content, small amount of space.  Dojo's Dijit library provides an incredibly simply method by which you can...

Discussion

  1. Enrique

    Hi, I think the useEffect() is not necessary:

    export function usePrevious(value) {
      const ref = useRef();
      const prev = ref.current;
      ref.current = value;
      return prev;
    }
    
    • Hazza

      The docs say not to set a ref during a render due to instability, useEffect ensures it runs after the render

  2. This and more are available in the excellent ahooks package: https://ahooks.js.org/hooks/state/use-previous.

  3. Saransh

    useLocalStorage. The one hook that I use a lot. Persisting filters of a table, search inputs, makes everything easy.

  4. /**
     * Disable the emoji's
     */
    function disable_emojis() {
     remove_action( 'wp_head', 'print_emoji_detection_script', 7 );
     remove_action( 'admin_print_scripts', 'print_emoji_detection_script' );
     remove_action( 'wp_print_styles', 'print_emoji_styles' );
     remove_action( 'admin_print_styles', 'print_emoji_styles' ); 
     remove_filter( 'the_content_feed', 'wp_staticize_emoji' );
     remove_filter( 'comment_text_rss', 'wp_staticize_emoji' ); 
     remove_filter( 'wp_mail', 'wp_staticize_emoji_for_email' );
     add_filter( 'tiny_mce_plugins', 'disable_emojis_tinymce' );
     add_filter( 'wp_resource_hints', 'disable_emojis_remove_dns_prefetch', 10, 2 );
    }
    add_action( 'init', 'disable_emojis' );
    
    /**
     * Filter function used to remove the tinymce emoji plugin.
     * 
     * @param array $plugins 
     * @return array Difference betwen the two arrays
     */
    function disable_emojis_tinymce( $plugins ) {
     if ( is_array( $plugins ) ) {
     return array_diff( $plugins, array( 'wpemoji' ) );
     } else {
     return array();
     }
    }
    
    /**
     * Remove emoji CDN hostname from DNS prefetching hints.
     *
     * @param array $urls URLs to print for resource hints.
     * @param string $relation_type The relation type the URLs are printed for.
     * @return array Difference betwen the two arrays.
     */
    function disable_emojis_remove_dns_prefetch( $urls, $relation_type ) {
     if ( 'dns-prefetch' == $relation_type ) {
     /** This filter is documented in wp-includes/formatting.php */
     $emoji_svg_url = apply_filters( 'emoji_svg_url', 'https://s.w.org/images/core/emoji/2/svg/' );
    
    $urls = array_diff( $urls, array( $emoji_svg_url ) );
     }
    
    return $urls;
    }
  5. Very interesting, Wish to see much more like this. Thanks for sharing your information!

Wrap your code in <pre class="{language}"></pre> tags, link to a GitHub gist, JSFiddle fiddle, or CodePen pen to embed!