JavaScript for(x in element) strange results
Alright, I'm trying开发者_如何学Python to use the basic document.getElementsByTagName function, but each time I do, it brings up results that don't exist. Ie: elements with undefined nodeNames, and things like this. This causes my script to halt, and is giving me quite the trouble.
Here is a sample:
This HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title></title>
</head>
<body>
<div></div>
<div></div>
<div></div>
</body>
</html>
with this script
for(x in document.getElementsByTagName('div'))
alert(document.getElementsByTagName('div')[x].nodeName);
generates this
DIV
DIV
DIV
undefined
then the script quits.
I cannot locate the issue, and it works like this in all browsers...
Just ask for any other details...
Correction: getElementsByTagName returns a NodeList, which has numeric indices and a length property, thereby making it an Array-like object.
Nevertheless, you should just use a simple for loop like so:
var els = document.getElementsByTagName('div');
for(var i = 0, j = els.length; i < j; i++) {
alert(els[i].nodeName);
The reason why you want to use for and not for..in here is because for..in uses inherited properties of the iterated object, so to avoid that you can use hasOwnProperty, but in this case where you're only iterating over a numeric indice, I think it's better to use a simple for loop over using for..in and hasOwnProperty.
Javascript returns all properties of the object when using for ( in ). Use .hasOwnProperty to skip inherited properties:
var elems = documents.getElementsByTagName('div');
for (x in elems){
if (elems.hasOwnProperty(x))
alert(elems[x].nodeName);
}
加载中,请稍侯......
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