Javascript checks whether the dom has been loaded.

First, we need to clarify two concepts

1. window. onload: After the page is loaded, all components (images, etc.) on the page are available.

2. dom loading: The file object model is loaded before the window. onload event.

It can be seen that when a page contains a large number of components (especially images), the loading time of the above two types will be very long, and it is particularly important to judge when the dom is loaded.

Some page components (css, image, flash) will not cause the page DOM to fail to be built. Only JS will block the construction of DOM nodes on the page

Function init (){

// If the function is called multiple times, the system returns

If (arguments. callee. done) return;

//

Arguments. callee. done = true;

// Clear the timer set for safari

If (_ timer) clearInterval (_ timer );

Alert (document. getElementById ("test"). id );

};

// Firefox and opera9.0

If (document. addEventListener ){

Document. addEventListener ("DOMContentLoaded", init, false );

}

// Ie

Document. write ("<script id = __ie_onload defer src = javascript: void (0)> <\/script> ");

Var script = document. getElementById ("_ ie_onload ");

Script. onreadystatechange = function (){

If (this. readyState = "complete "){

Init (); // call the onload handler

}

};

// Safari

If (/WebKit/I. test (navigator. userAgent) {// sniff

Var _ timer = setInterval (function (){

If (/loaded | complete/. test (document. readyState )){

Init (); // call the onload handler

}

}, 10 );

}

// Other browsers directly use the window. onload event

Window. onload = init;

Source: http://www.wellpeter.com /? P = 162