mirror of
https://github.com/FAUSheppy/javascript-lazyload
synced 2025-12-06 04:11:35 +01:00
95 lines
3.0 KiB
JavaScript
Executable File
95 lines
3.0 KiB
JavaScript
Executable File
/* determine which size of image to load */
|
|
function getSize(){
|
|
var trueRes = screen.width/window.devicePixelRatio
|
|
if(trueRes > 1920)
|
|
return '-640-480'
|
|
else if(trueRes <= 1920 && trueRes >= 1200)
|
|
return '-640x480'
|
|
else
|
|
return '-320x240'
|
|
}
|
|
|
|
/* check if browser is capable of webp */
|
|
function supportsWebp() {
|
|
return /Chrome/.test(navigator.userAgent) && /Google Inc/.test(navigator.vendor);
|
|
|
|
/* alternative to check for webP support */
|
|
//if (!self.createImageBitmap) return false;
|
|
//const webpData = 'data:image/webp;base64,UklGRh4AAABXRUJQVlA4TBEAAAAvAAAAAAfQ//73v/+BiOh/AAA=';
|
|
//return createImageBitmap(webpData).then(() => true, () => false);
|
|
}
|
|
|
|
/* cache */
|
|
var webP = supportsWebp()
|
|
var elements = null
|
|
var counter = 0
|
|
|
|
/* garantuee initall call evaluates to true */
|
|
var viewbox_y = -Infinity
|
|
|
|
IDENT = "realsrc"
|
|
|
|
/* function to load images */
|
|
function changeSrc(offset){
|
|
|
|
/* check if there was a relevant change */
|
|
var cur_viewbox = -document.getElementById("navbar").getBoundingClientRect().y
|
|
if(cur_viewbox - viewbox_y < 100){
|
|
return;
|
|
|
|
}
|
|
|
|
/* cache viewbox */
|
|
viewbox_y = cur_viewbox
|
|
|
|
/* cache */
|
|
if(elements == null){
|
|
elements = document.querySelectorAll("*[" + IDENT + "]");
|
|
}
|
|
|
|
for (var i = counter; i < elements.length; i++) {
|
|
var boundingClientRect = elements[i].getBoundingClientRect();
|
|
if (elements[i].hasAttribute(IDENT)
|
|
&& boundingClientRect.top < window.innerHeight + offset) {
|
|
|
|
var newSrc = elements[i].getAttribute(IDENT)
|
|
/* remove url( ... ) if it is used */
|
|
//newSrc = newSrc.substring(4,newSrc.length-1)
|
|
|
|
if(newSrc.indexOf(".jpg") > -1){
|
|
/* get correct size */
|
|
newSrc += getSize()
|
|
|
|
/* load webP if supported */
|
|
if(webP){
|
|
newSrc = newSrc + '.webp'
|
|
}
|
|
}
|
|
elements[i].setAttribute("src", newSrc);
|
|
elements[i].style.backgroundImage = 'url(' + newSrc +')';
|
|
elements[i].removeAttribute(IDENT);
|
|
}else{
|
|
/* DOM is parsed top down and images are inserted in that order too */
|
|
/* meaing that once we reach pic that insnt in viewbox none following will be*/
|
|
counter = i;
|
|
return;
|
|
}
|
|
}
|
|
|
|
/* if we got here we are done */
|
|
document.getElementById("main_scrollable").removeEventListener("scroll",refresh_handler);
|
|
|
|
}
|
|
var refresh_handler = function(e) {
|
|
/* images directly in view first (offset 0)*/
|
|
//changeSrc(0)
|
|
/* then load images almost in view */
|
|
changeSrc(500)
|
|
};
|
|
|
|
/* add listeners */
|
|
document.getElementById("main_scrollable").addEventListener('scroll', refresh_handler);
|
|
window.addEventListener('resize', refresh_handler);
|
|
window.addEventListener('load', refresh_handler);
|
|
getSize()
|