Is this right? A jQuery bug that erases the data store?
javascript, jquery
Solution
Why is there ultimately any difference?
Both `thisx` and `this.x` are evaluated when the function is called. The first one refers to an undefined variable name and this throws a reference error. The second one accesses an undefined property of an object, which results in the value `undefined`. This is just how javascript behaves in these cases.
Now when JQuery is called in the second case, the call `$(this.x)` evaluates to `$(undefined)` which is the same as if you just would have called `$()`. Since it looks to JQuery as if no argument was provided, it uses a default instead, and in this case the default is `document`. Then it proceeds trying to delete `document`, since it was effectively called as `$().remove()`, in which case this would be expected.
Suggestions for how to handle this?
The difference with the `ReferenceError` is a fundamental Javascript difference, not much that can be done about that. JQuerys behavior is unfortunate and a consequence of setting defaults by `arg = arg||default`. One could user `arguments.length` instead to get the real number of call parameters, but a change like this would surely result in lot's of broken code that relied on the default being used when `undefined` or `0` is passed, so it's unlikely to happen.
Problem
Fire up your firebug console and try this out. Compare this: ``` $('body').data('x',1); $(thisx).remove(); console.log($('body').data('x')); ``` to this: ``` $('body').data('x',1); $(this.x).remove(); console.log($('body').data('x')); ``` Notice the difference? If `thisx` is undefined, it will immediatly throw a reference error. If `x` is an undefined property of `this`, jQuery will return the document as it's result set instead. Next jQuery will attempt to remove your document (which it can't), but before doing that it will remove all data attached to any child element of the document. Thus, wiping out your data store. Note: `this` can be any element reference or object. You only need to have jQuery attempt to access an undefined property. (Talk about a pain. It fails silently, and I'm trying to figure out why my data is suddenly missing. I track it down to a special case where an element reference was undefined in a specific situation.) So on to my questions: 1) Before I submit a bug report, am I analyzing this correctly? Also if someone happens to know that this is a known issue, let me know. I couldn't find it in the bug tracker, but the interface isn't that great (or maybe I have this wrong). 2) Why is there ultimately any difference? I'm guessing `thisx` is evaluated immediately which causes the exception while `this.x` is a reference that is passed and evaluated in the called function, right? (where I think the line `selector = selector || document`; is the culprit. 3) Suggestions for how to handle this? I guess I should be checking that any/every element reference or property of an object (e.g. stored selector strings) is defined before I pass it to jQuery when removing something.