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!function(a,b){"function"==typeof define&&define.amd?define(b):"object"==typeof exports?module.exports=b:a.echo=b(a)}(this,function(a){"use strict";var b,c,d,e,f={},g=function(){},h=function(a,b){var c=a.getBoundingClientRect();return c.right>=b.l&&c.bottom>=b.t&&c.left<=b.r&&c.top<=b.b},i=function(){clearTimeout(c),c=setTimeout(f.render,d)};return f.init=function(c){c=c||{};var h=c.offset||0,j=c.offsetVertical||h,k=c.offsetHorizontal||h,l=function(a,b){return parseInt(a||b,10)};b={t:l(c.offsetTop,j),b:l(c.offsetBottom,j),l:l(c.offsetLeft,k),r:l(c.offsetRight,k)},d=l(c.throttle,250),e=!!c.unload,g=c.callback||g,f.render(),document.addEventListener?(a.addEventListener("scroll",i,!1),a.addEventListener("load",i,!1)):(a.attachEvent("onscroll",i),a.attachEvent("onload",i))},f.render=function(){for(var c,d,i=document.querySelectorAll("img[data-echo]"),j=i.length,k={l:0-b.l,t:0-b.t,b:(a.innerHeight||document.documentElement.clientHeight)+b.b,r:(a.innerWidth||document.documentElement.clientWidth)+b.r},l=0;j>l;l++)d=i[l],h(d,k)?(e&&d.setAttribute("data-echo-placeholder",d.src),d.src=d.getAttribute("data-echo"),e||d.removeAttribute("data-echo"),g(d,"load")):e&&(c=d.getAttribute("data-echo-placeholder"))&&(d.src=c,d.removeAttribute("data-echo-placeholder"),g(d,"unload"));j||f.detach()},f.detach=function(){document.removeEventListener?a.removeEventListener("scroll",i):a.detachEvent("onscroll",i),clearTimeout(c)},f});
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