Analyze page loading and js function execution onload or ready_jquery

First, the page loading sequence:
Parse the HTML structure.
Load external scripts and stylesheet files.
Parse and execute script code.
Construct HTML DOM model.
Load external files such as images.
The page is loaded.

That is:
html → head → title → #text (webpage title) → style → load style → parse style → link → load external style sheet file → parse external style sheet → script → load external script file→ Parse the external script file → execute the external script → body → div → script → load the script → parse the script → execute the script → img → script → load the script → parse the script → execute the script → load the external image file → the page initialization is completed.

Initial loading of JS.

onload
is not called when the document is loaded, but is called when all elements of the page (including images, etc.) are loaded. If the page If there are large-sized images that take a long time to download, then the script cannot be initialized until the image is loaded. In severe cases, the user experience will be greatly affected. However, window.onload is not useless in many cases. Some B/S software requires that the page be fully loaded before providing user-related functions, so window.onload can provide a "loading" function, or the page content is very small, and document.ready() is not needed at all; according to In various situations, onload and ready should be used appropriately.

Use onload to load:

Copy code The code is as follows:

window.onload=function (){
var currentRenderer = 'javascript'; swfUrl: "Pie3D.swf",
swfUrl: " 290", height: "210",
          id: 'sampleChart',
                                                                                        dataFormat: FusionChartsDataFormats .


There is an event called DOMContentLoaded in W3C, which is triggered when the DOM (Document Object Model) is loaded.


Method 1:

Copy the code
The code is as follows:

Similar to Jquery's $(function(){...}) $(document).ready(function(){...})
(function () {var ie = !!(window. attachEvent && !window.opera);

var wk = /webkit/(d )/i.test(navigator.userAgent) && (RegExp.$1 < 525);var fn = [];var run = function () { for (var i = 0; i < fn.length; i ) fn[i](); };var d = document;d.ready = function ( f) {if (!ie && !wk && d.addEventListener)return d.addEventListener('DOMContentLoaded', f, false);

if (fn.push(f) > 1) return;

if (ie)
(function () {
try { d.documentElement.doScroll('left'); run(); }
catch (err) { setTimeout(arguments. callee, 0); }
})();
else if (wk)
var t = setInterval(function () {
if (/^(loaded|complete)$/.test (d.readyState))
clearInterval(t), run();
}, 0);
};
})();


when called ：
document.ready(function(){
alert('ok');
}


Method 2:

Copy the code


The code is as follows:

/If W3C DOM2 is supported, use the W3C method
if (document.addEventListener){
document.addEventListener("DOMContentLoaded", te, false);
}
else if (/MSIE/i.test(navigator.userAgent)){/If it is IE browser (not supported)
/Create a script tag, which has a defer attribute and will be loaded when the document is loaded.
document.write("
var script = document.getElementByIdx_x("__ie_onload");
/If the document is indeed loaded, call the initialization method
script.onreadystatechange = function() {
if (this.readyState == 'complete') {
te();
} }
}
}
else if (/WebKit/i.test(navigator.userAgent)) { /If it is Safari browser (not supported)
/Create a timer, check every 0.01 seconds, and call the initialization method if the document is loaded
var _timer = setInterval( function() {
if (/ loaded|complete/.test(document.readyState)) {
                                                                                                                                                                   If none of the above, use the worst option (in this case, Opera 7 will run here)
window.onload = function(e) {
te();
}
}
function te(){
alert('ok');
}