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问题:

So I'm learning to manipulate the DOM and I noticed one interesting thing:

Let's say I want to set the name attribute of an element by using the "." dot notation:

element.name = "someName";
console.log(document.getElementsByName("someName")[0]); // returns "undefined"??

However if I use the document.setAttribute() method, it works fine:

element.setAttribute("name", "someName");
console.log(document.getElementsByName("someName")[0]); // returns the element like it should.

Not sure why the dot notation method doesn't work in the first case.

Why does this happen?

回答1:

My guess (because you didn't specify the element type) is the element normally does not have a name attribute, so setting the DOM property like that won't work.

For example, setting the name property on an input element will work. Setting it on a div will not.

It will work, however, with setAttribute().

jsFiddle.

回答2:

To extend the answers provided by some of the others ...

The attribute 'name' is only considered valid DOM for a few specific objects. According to https://developer.mozilla.org/en-US/docs/DOM/element.name those objects are:

 <a>, <applet>, <button>, <form>, <frame>, <iframe>, <img>, <input>, 
 <map>, <meta>, <object>, <param>, <select>, and <textarea>

For these objects you can set, get and change the name attribute using object.name BUT FOR ANY OTHER DOM OBJECT the attribute 'name' is a custom attribute and must be created using SetAttribute() or by adding it to the HTML declaration. Once it is created, you can acces it using setAttribute() and getAttribute() or you can refer to its value directly using object.attributes.name.value take a look at http://jsfiddle.net/radiotrib/yat72/1/ for an example. BTW - the alert box on load is intentional - check the code to see why ...

回答3:

(Attempting to explain part of the above post a better, separately, since it is already went into -ve rating, and belief in that post will be less. Help improve this further.)

*** The property

When you use, element.name, you are accessing a existing property named "name" or setting its value.

Example 1:
var div1 = document.getElementById("div1"); 
div1.textContent = "2";

*** The attribute

but, while using, element.setAttribute('name','someName'), you are actually setting the attribute named 'name'. This attribute can be an existing property too

Example 2:
var h1 = document.getElementById("H1"); 
h1.setAttribute("class", "democlass");

Example 3:
var d = document.getElementById("d1"); 
d.setAttribute("name1", "value1");

回答4:

when you use, element.name, you are accessing the property/creating a property named "name" and setting its value.

回答5:

when you use, element.name, you are accessing the property/creating a property named "name" and setting its value.

but,

while using, element.setAttribute('name','someName'), you are actually setting the attribute 'name'.

IE8 and below treats the property and attribute as same, the bug has been fixed in IE9 and above.
Safari, FireFox, Chrome treat property and attribute differently.

However, you can always create a new property of your choice if you wish to do so.

回答6:

<head>
<script>
function test($count) {
document.getElementById("test1").setAttribute("name","file-upload_" + $count);
}
</script>
</head>
<body>

<p>some content</p>
<input id="test1" type="file" name="file-upload" id="file-upload" />
<p>some other content</p>
<script>test(1);</script>
</body>