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Increase lazy loader performance 

This stops the checkElementsInView method from running when there aren't any lazy load images on the page. By calling this method we are causing an unnecessary reflow which on large pages is a massive performance issue
This commit is contained in:
Phil Hughes 2017-10-31 17:18:09 +00:00
parent b86c3a7365
commit 1f60cd8cd7
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GPG Key ID: 32245528C52E0F9F
1 changed files with 7 additions and 8 deletions
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15
app/assets/javascripts/lazy_loader.js
View File

@ -1,5 +1,3 @@
/* eslint-disable one-export, one-var, one-var-declaration-per-line */
import _ from 'underscore';
export const placeholderImage = 'data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==';
@ -21,7 +19,10 @@ export default class LazyLoader {
}
searchLazyImages() {
this.lazyImages = [].slice.call(document.querySelectorAll('.lazy'));
this.checkElementsInView();
if (this.lazyImages.length) {
this.checkElementsInView();
}
}
startContentObserver() {
const contentNode = document.querySelector(this.observerNode) || document.querySelector('body');
@ -45,15 +46,13 @@ export default class LazyLoader {
checkElementsInView() {
const scrollTop = pageYOffset;
const visHeight = scrollTop + innerHeight + SCROLL_THRESHOLD;
let imgBoundRect, imgTop, imgBound;
// Loading Images which are in the current viewport or close to them
this.lazyImages = this.lazyImages.filter((selectedImage) => {
if (selectedImage.getAttribute('data-src')) {
imgBoundRect = selectedImage.getBoundingClientRect();
imgTop = scrollTop + imgBoundRect.top;
imgBound = imgTop + imgBoundRect.height;
const imgBoundRect = selectedImage.getBoundingClientRect();
const imgTop = scrollTop + imgBoundRect.top;
const imgBound = imgTop + imgBoundRect.height;
if (scrollTop < imgBound && visHeight > imgTop) {
LazyLoader.loadImage(selectedImage);