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lazy-load-images.js
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lazy-load-images.js
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import { throttle } from 'lodash'
function inViewport (element) {
const { top, right, bottom, left } = element.getBoundingClientRect()
return bottom > 0 &&
window.innerWidth - left > 0 &&
window.innerHeight - top > 0 &&
right > 0
}
module.exports = function () {
['scroll', 'resize', 'load'].forEach(event =>
window.addEventListener(event, updateImages)
)
// add all images that are part of the DOM tree
// NB: |display: none| elements need manual adding
document.querySelectorAll('img[data-src]').forEach(addImage)
}
let images = []
const addImage = module.exports.addImage = function (image) {
// abort if this element has previously entered the viewport
if (!image.dataset.src) return
images.push(image)
updateImages()
}
function loadImage (image) {
// abort if this element has entered the viewport after added to the list
if (!image.dataset.src) return
image.setAttribute('src', image.dataset.src)
// remove attribute so CSS fade-in can happen
image.onload = () => {
image.removeAttribute('data-src')
// remove colored circular placeholder element
const placeholder = image.parentElement.querySelector('.placeholder')
if (placeholder) placeholder.classList.add('faded-out')
}
}
const updateImages = module.exports.updateImages = throttle(() => {
images = images.filter(image => {
if (inViewport(image)) {
loadImage(image)
return false // remove from unseen photos
}
return true // keep in unseen photos
})
}, 100)