body-scroll-freezer


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

Useful for modal, sliding-panel and lightbox interfaces.

> <1kb minified.

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 .
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.

Usage

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

1\. Init to calculate scroll bar width.

`js
// Note: declaring variable to store init() return is optional.
var scrollWidth = bodyScroll.init();
`

2\. Turn scroll freeze ON when closing modal. Example:

`js
document.querySelector('.modal-open').addEventListener('click', function() {
// Logic to show modal goes here
bodyScroll.freeze();
}, false);
`

3\. Turn scroll freeze OFF when closing modal. Example:

`js
document.querySelector('.modal-close').addEventListener('click', function() {
// Logic to hide modal goes here
bodyScroll.unfreeze();
}, false);
``