Dependency-free JS module to freeze body scroll when opening modal box

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2221.0.57 years ago7 years agoMinified + gzip package size for body-scroll-freezer in KB


npm version
Dependency-free JS module to freeze body scroll when opening modal box.
Useful for modal, sliding-panel and lightbox interfaces.
<1kb minified.

body-scroll-freezer: online demo

A note on performance

Many other alternatives to this module listen to both mousewheel and DOMMouseScroll events in order to get some information from the DOM, which usually includes: Element.scrollTop, event.deltaY, Element.scrollHeight or Element.clientHeight. Check this StackOverflow answer as an example.
The problem is that most of those DOM operations (.scrollTop and .scrollHeight, for example) are expensive because they force layout/reflow. For more info on scrolling performance check out this article.
So, to avoid all that, body-scroll-freezer just assigns overflow: hidden; and padding-right: [scrollWidth]px; to the <body>. The overflow avoids vertical move on the background when users are scrolling within the modal box. The padding-right prevents horizontal jumps when hiding/showing the scrollbar.


// If no AMD/CommonJS: window.bodyScrollFreezer;
var bodyScroll = require('body-scroll-freezer'); 

1\. Init to calculate scroll bar width.
// Note: declaring variable to store init() return is optional.
var scrollWidth = bodyScroll.init();

2\. Turn scroll freeze ON when closing modal. Example:
document.querySelector('.modal-open').addEventListener('click', function() {
  // Logic to show modal goes here
}, false);

3\. Turn scroll freeze OFF when closing modal. Example:
document.querySelector('.modal-close').addEventListener('click', function() {
  // Logic to hide modal goes here
}, false);