Question

if a == "http://foo.bar"
and $(b[0]).attr("href") == "http://foo.bar"

then why does the following code not return true:

$("[href^=\"" + a + "\"]", b).length > 0

?

Answer 1

Because the second parameter passed to the jQuery function scopes the selector, which is to say, find the selected element in the children of b.

So by way of an example

<div id="one">
   <div id="two" title="Test" />
</div>

This will return 1

$('[title="Test"]','#one').length 

This will return 0

$('[title="Test"]','#two').length 

Live example: http://jsfiddle.net/mkudf/

---

Based on your comments, it seems you’re doing some stuff before adding the element to the dom, so by example:

var $x = $('<div id="one" /><div id="two" title="Test" />');
alert($('[title="Test"]',$x).length); // alerts "0"

I can find no way of achieving what you want (The above to alert “1”) without wrapping the dynamic elements in an extra element:

var $x = $('<div><div id="one" /><div id="two" title="Test" /></div>');
alert($('[title="Test"]',$x).length); // now alerts "1"

Which shouldnt be too much of a problem, when adding to the dom you could just take $x.children():

$someOtherElement.after($x.children());