This is expected behaviour.

Pull request with fix: https://github.com/jquery/jquery/pull/392

Why is it expected behavior? It breaks chaining and causes unexpected exceptions.

It's expected that the developer knows to test their own variables before passing them to methods that have overloaded signatures.

var text;
$("<div/>").text( text || "" ).append($("<span/>"))

http://jsfiddle.net/rwaldron/sTesj/

The code above will work fine without breaking the existing api.

As noted on the pull request: http://api.jquery.com/text/ The documentation specifies the valid input to the method and their expected outcome.

FWIW, I would recommend using this work around instead:

#!js
var text;
$("<div/>").text( text + "" ).append($("<span/>"));

It handles 0 and null better and saves 1 byte.

Also, FWIW, this bug also affects $.fn.html, $.fn.attr, $.fn.width, $.fn.height, and number other functions.

I replied to http://bugs.jquery.com/ticket/5571, but it might be worth repeating my argument here. Basically, I feel that the getter/setter functionality should be determined by arguments.length instead of the argument values. IMO, this leads to a more consistent API and is less surprising to the user.

There is the argument that undefined is an invalid value, so breaking the chain makes sense since it acts like a form of error reporting. I disagree with this logic. As a form of error reporting, breaking the chain doesn't always work and leads to confusing error messages. (See ticket for more detailed explanation).

#9826 is a duplicate of this ticket.

I agree that this is a bug, arity > 1 shows the intention

#10396 is a duplicate of this ticket.

#10671 is a duplicate of this ticket.

#10749 is a duplicate of this ticket.

Reopening for 1.8 discussion -- should we have uniform behavior for .method(undefined/null) ?

We landed this space-saving bug fix in https://github.com/jquery/jquery/commit/6c2a501de40a5f6b3ad382e2d309e5a10fce04d0

text + ""

text || ""

Note that these two have different behavior in cases other than those you've considered. If text is an empty array, for example, the previous effective value would have been [], while in jQuery 1.7.2 it becomes "[object Object]".

It appears that .text([]) is a no-op in jQuery pre-1.7.2. Some of my code was unknowingly relying on this behavior, and broke when I upgraded to 1.7.2. I'm fixing the code in question, which shouldn't be passing [] to text() in the first place. But I figured you might want to know about this, since it does represent an undocumented change, however minor.