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for web browser have only one thread.while loading or execute js, the UI update will be blocked.some way to improve
1.put js before </body> tag.so js will be loaded and run after page have been fully loaded.
2.orangize script.combine some script to one to reduce HTTP request.
3 no blocked js. loading js after window.onload run or DOMContentedloaded run.
4 ***dynamic script
use async script
some tip http://stackoverflow.com/questions/33470619/why-script-dom-element-can-be-async-loading/33471838#33471838
var script=document.createElement(‘script‘);
script.src=‘aa.js‘;
document.getElementByTagName(‘head‘)[0].appendChild(script);
this way, js will run as soon as loaded.if js need other api,we need to make sure api is run before this js code. so sequence of script is important.
for w3c.we use one of attribute of script,onload to test if script has fully loaded.
script.onload=function(){
alert(‘loaded‘);
}
but for IE, we use readystatechange event;
it has 4 state, state loaded and state4 complete important.
but not sure which will happen first.if one of two happened,means script fully loaded.one of state run ,we cancel the event;we use
script.onreadystatechange=function(){
if(script.readyState===‘complete‘ || script.readyState===‘loaded‘){
script.onreadystatechange=null;
alert(‘loaded‘);
}
}
and combine two to one can make cross browser version.
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原文地址：http://www.cnblogs.com/wz0107/p/4960127.html
