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lozad.js
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lozad.js
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/**
* Detect IE browser
* @const {boolean}
* @private
*/
const isIE = typeof document !== 'undefined' && document.documentMode
/**
*
* @param {string} type
*
*/
const support = type => window && window[type]
const validAttribute = ['data-iesrc', 'data-alt', 'data-src', 'data-srcset', 'data-background-image', 'data-toggle-class']
const defaultConfig = {
rootMargin: '0px',
threshold: 0,
enableAutoReload: false,
load(element) {
if (element.nodeName.toLowerCase() === 'picture') {
let img = element.querySelector('img')
let append = false
if (img === null) {
img = document.createElement('img')
append = true
}
if (isIE && element.getAttribute('data-iesrc')) {
img.src = element.getAttribute('data-iesrc')
}
if (element.getAttribute('data-alt')) {
img.alt = element.getAttribute('data-alt')
}
if (append) {
element.append(img)
}
}
if (element.nodeName.toLowerCase() === 'video' && !element.getAttribute('data-src')) {
if (element.children) {
const childs = element.children
let childSrc
for (let i = 0; i <= childs.length - 1; i++) {
childSrc = childs[i].getAttribute('data-src')
if (childSrc) {
childs[i].src = childSrc
}
}
element.load()
}
}
if (element.getAttribute('data-poster')) {
element.poster = element.getAttribute('data-poster')
}
if (element.getAttribute('data-src')) {
element.src = element.getAttribute('data-src')
}
if (element.getAttribute('data-srcset')) {
element.setAttribute('srcset', element.getAttribute('data-srcset'))
}
let backgroundImageDelimiter = ','
if (element.getAttribute('data-background-delimiter')) {
backgroundImageDelimiter = element.getAttribute('data-background-delimiter')
}
if (element.getAttribute('data-background-image')) {
element.style.backgroundImage = `url('${element.getAttribute('data-background-image').split(backgroundImageDelimiter).join('\'),url(\'')}')`
} else if (element.getAttribute('data-background-image-set')) {
const imageSetLinks = element.getAttribute('data-background-image-set').split(backgroundImageDelimiter)
let firstUrlLink = (imageSetLinks[0].substr(0, imageSetLinks[0].indexOf(' ')) || imageSetLinks[0]) // Substring before ... 1x
firstUrlLink = firstUrlLink.indexOf('url(') === -1 ? `url(${firstUrlLink})` : firstUrlLink
if (imageSetLinks.length === 1) {
element.style.backgroundImage = firstUrlLink
} else {
element.setAttribute('style', (element.getAttribute('style') || '') + `background-image: ${firstUrlLink}; background-image: -webkit-image-set(${imageSetLinks}); background-image: image-set(${imageSetLinks})`)
}
}
if (element.getAttribute('data-toggle-class')) {
element.classList.toggle(element.getAttribute('data-toggle-class'))
}
},
loaded() {}
}
function markAsLoaded(element) {
element.setAttribute('data-loaded', true)
}
function preLoad(element) {
if (element.getAttribute('data-placeholder-background')) {
element.style.background = element.getAttribute('data-placeholder-background')
}
}
const isLoaded = element => element.getAttribute('data-loaded') === 'true'
const onIntersection = (load, loaded) => (entries, observer) => {
entries.forEach(entry => {
if (entry.intersectionRatio > 0 || entry.isIntersecting) {
observer.unobserve(entry.target)
if (!isLoaded(entry.target)) {
load(entry.target)
markAsLoaded(entry.target)
loaded(entry.target)
}
}
})
}
const onMutation = load => entries => {
entries.forEach(entry => {
if (isLoaded(entry.target) && entry.type === 'attributes' && validAttribute.indexOf(entry.attributeName) > -1) {
load(entry.target)
}
})
}
const getElements = (selector, root = document) => {
if (selector instanceof Element) {
return [selector]
}
if (selector instanceof NodeList) {
return selector
}
return root.querySelectorAll(selector)
}
export default function (selector = '.lozad', options = {}) {
const {root, rootMargin, threshold, enableAutoReload, load, loaded} = Object.assign({}, defaultConfig, options)
let observer
let mutationObserver
if (support('IntersectionObserver')) {
observer = new IntersectionObserver(onIntersection(load, loaded), {
root,
rootMargin,
threshold
})
}
if (support('MutationObserver') && enableAutoReload) {
mutationObserver = new MutationObserver(onMutation(load, loaded))
}
const elements = getElements(selector, root)
for (let i = 0; i < elements.length; i++) {
preLoad(elements[i])
}
return {
observe() {
const elements = getElements(selector, root)
for (let i = 0; i < elements.length; i++) {
if (isLoaded(elements[i])) {
continue
}
if (observer) {
if (mutationObserver && enableAutoReload) {
mutationObserver.observe(elements[i], {subtree: true, attributes: true, attributeFilter: validAttribute})
}
observer.observe(elements[i])
continue
}
load(elements[i])
markAsLoaded(elements[i])
loaded(elements[i])
}
},
triggerLoad(element) {
if (isLoaded(element)) {
return
}
load(element)
markAsLoaded(element)
loaded(element)
},
observer,
mutationObserver
}
}