如何知道HTML元素何时准备就绪（呈现）？

Question

I have some javascript that adds an element to the document. Immediately after adding i am trying to obtain the element's clientWidth and clientHeight. However I am seeing all properties related to size to be 0. But at a later point i notice that the size properties do get populated with actual size values (eventually).

How can I know when the size details are available for an added Html element? I have tried listening to various events, such as onload and onreadystatechange. However these events seem to only apply for the document itself, not for individual elements.

Thanks much.

Answer 1

DOM changes are postponed until the javascript thread quits, therefore this doesn't work:

someNode.addChild(someElem);
w = someElem.clientWidth // 0

You have to start a new thread in order to work with newly added element:

someNode.addChild(someElem);

setTimeout(function() {
     w = someElem.clientWidth // should work
}, 0)

Alternatively (and better), try listening to a DOM mutation event:

document.body.addEventListener('DOMNodeInserted', function(e) {
    alert('div height=' + e.target.clientHeight)
})

d = document.createElement("div")
d.appendChild(document.createTextNode("hello"))
t = document.body.appendChild(d)

http://jsfiddle.net/rM5cJ/

Answer 2

You could set an initial dictionary (object literal can be used)— where you set at the very first start of the document , and after each html being rendered you can do :

<div id='aaa'> </div>

<Script>myObject.Add('aaa',1,doSomethingLater) </script>

You can not use the onload event since it's relevant only for : img / body/iframes.

The object can look like this :

myObject =
{
 Add:function (a,b,cb){this[a]=b;cb(a,b)} 

}