I came across a bug in Internet Explorer whereby the document.getElementById() function may return an element with a name attribute equal to the id that is specified. This can cause unexpected results.
According to the W3C’s DOM Level 2 Core Specification:
getElementById
introduced in DOM Level 2Returns the Element
whoseID
is given byelementId
. If no such element exists, returnsnull
. Behavior is not defined if more than one element has thisID
.Note: The DOM implementation must have information that says which attributes are of type ID. Attributes with the name “ID†are not of type ID unless so defined. Implementations that do not know whether attributes are of type ID or not are expected to return
null
.Parameters
elementId
of typeDOMString
- The unique
id
value for an element.Return Value
Element
The matching element. No Exceptions
http://www.w3.org/TR/DOM-Level-2-Core/core.html#ID-getElBId
However, for the browsers that failed the test, it appears that their implimentation of getElementById returns the first element where the ID or name attribute is equal to the specified ID.
This bug was tested against the following browsers:
- IE 6.0 sp2: failed
- IE 5.5: failed
- IE 5.01: failed
- Netscape 7.2: passed
- Netscape 6: passed
- Mozilla 1.7.3: passed
- Opera 8.2: failed
- Firefox 1.0.6: passed
For instance, the following code should produce an alert with “foo=foo; bar=barâ€. However, the browsers that fail the test actually return “foo=foo; bar=fooâ€.
<form name="form1" id="form1" method="get" action="javascript: void(0)">
<input name="bar" type="text" id="foo" value="foo" /><br />
<input name="foo" type="text" id="bar" value="bar" readonly="readonly" /><br />
<input type="button" name="Button" value="Test" onclick="alert(’foo=’+document.getElementById(’foo’).value+’; bar=’+document.getElementById(’bar’).value)" /><br />
</form>
Reported at http://www.quirksmode.org/bugreports/index.html 2005-08-29
Noted on http://channel9.msdn.com/wiki/default.aspx/Channel9.InternetExplorerProgrammingBugs
* This post was originally published on August 29, 2005 at http://www.csb7.com/whyblogwhy/index.php/2005/08/29/ie_getelementbyid_bug/