August 05, 2020ย ย โ€ขย ย 1 min read

#5 hook of the week

To remind you of the purpose and goal of this week:

For a whole week I'll post a new hook every day. All hooks will support Server-Side Rendering (SSR) and have TypeScript implemented.

I will not describe the hooks in great detail, I'll just present them and show how it's implemented. Then you can do whatever you want with them.

Every hook is also available here, together with a range of other hooks.

View source

Showcase ๐Ÿ”ฅ

This website only uses two breakpoints, these are xs (480px) and sm (768px). Resize your browser window between these breakpoints and you'll see it change below.

Current breakpoint:


A common issue between non CSS-in-JS styling and JavaScript is shared breakpoints. You want the css and js to listen to the same collection of breakpoints.

I will show you a way of doing so with SCSS and JavaScript.

Define breakpoints

We'll define the collection of breakpoints within a SCSS map and expose it to the <body>.

// Define breakpoints
$breakpoints: (
  sm: 768px,
  md: 992px,
  lg: 1200px

// Simple media query mixin
@mixin respond-to($breakpoint) {
  @media (min-width: #{map-get($breakpoints, $breakpoint)}) {

// Expose breakpoints
body::after {
  position: absolute;
  left: -1337px;
  visibility: hidden;
  user-select: none;
  pointer-events: none;
  opacity: 0;
  font-size: 0;
  z-index: -1;

  @each $breakpoint-key, $breakpoint-value in $breakpoints {
    @if ($breakpoint-key == 'sm') {
      content: 'sm';
    } @else {
      @include respond-to($breakpoint-key) {
        content: '#{$breakpoint-key}';

If you inspect the source code of this website you'll see this logic in use.

The hook ๐ŸŽฃ

With this hook we can communicate the use of breakpoints between SCSS and JavaScript.

I'm using my isSSR utility and useWindowSize() hook to get the breakpoint.

import { useEffect, useState, useCallback } from 'react';
import { isSSR } from './utils';
import { useWindowSize } from './useWindowSize';

export const useBreakpoint = (): string | undefined => {
  const { width } = useWindowSize();
  const getBreakpoint = useCallback(
    () =>
        ? undefined
        : window
          .getComputedStyle(document.body, '::after')
          .content.replace(/"/g, ''),
  const [breakpoint, setBreakpoint] = useState(getBreakpoint);

  useEffect(() => {
  }, [width, getBreakpoint]);

  return breakpoint;


When the breakpoint changes we'll console.log() it.

import React, { useEffect } from 'react';
import { useBreakpoint } from './useBreakpoint';

const Component = () => {
  const breakpoint = useBreakpoint();

  useEffect(() => {
  }, [breakpoint]);

  return null;

export default Component;

The end ๐Ÿ’”

I hope you found this helpful.