README.md

conditional-breakpoint.js

Reduce handling overhead of the scroll and resize events by triggering a handler only once on passing a breakpoint.

Browsers support

Every browser that has window.addEventListener() is supported (IE9+).

Installation

Bower

bower install conditional-breakpoint

NPM

npm install conditional-breakpoint

Usage

Let's add the sticky-header class to the body element as soon as the scroll position > 500 pixels and remove it otherwise.

window.conditionalBreakpoint.scroll(
  () => window.scrollY > 500,
  // This fn is called when the boolean of the above callback changes.
  (isTrue) => document.body.classList[isTrue ? 'add' : 'remove']('sticky-header'),
);

Tip

The window.conditionalBreakpoint.resize() is also available with the exact same calling signature.

Use the above instead of this:

window.addEventListener(
  'scroll',
  // This fn is called on every scroll movement.
  () => document.body.classList[this.scrollY > 500 ? 'add' : 'remove']('sticky-header'),
);

Two examples above technically do the same job however the first one runs a handler only on reaching a condition and then waits for it to change to run again. This allows separating the handling logic from a condition check to gain some performance. Contrary, the standard event handler do a condition check and run the logic on every event occurrence.

Check out the demo