Undefined test not working in javascript

Question

I'm getting the error 'foo' is undefined. in my script when i test my function with an undefined parameter. As far as I understand, This shouldn't be happening.

My calling code:

//var foo
var test = peachUI().stringIsNullOrEmpty(foo) ;

My function (part of a larger framework).

    stringIsNullOrEmpty: function (testString) {
        /// <summary>
        ///     Checks to see if a given string is null or empty.
        /// </summary>
        /// <param name="testString" type="String">
        ///     The string check against.
        /// </param>
        /// <returns type="Boolean" />

        var $empty = true;

        if (typeof testString !== "undefined") {
            if (testString && typeof testString === "string") {

                if (testString.length > 0) {
                    $empty = false;
                }

            }
        }
        return $empty;
    }

Any ideas?

Please note. I've had a good read of other similar questions before posting this one.

Nick Craver · Accepted Answer · 2010-12-24 11:50:02Z

2

You can't pass a variable that doesn't exist (undefined, not null...which does exist) into a function, it's trying to get the value of foo to pass it when you call

var test = peachUI().stringIsNullOrEmpty(foo);

...and it isn't there, so you're getting the error on just that line, just as you would with a simpler case:

alert(foo);

Now if you tried to call it as a property of something, then it'd be valid, for example:

alert(window.foo);

Then undefined gets passed in, because it's an undefined property on a known/present object.

answered Dec 24, 2010 at 11:50

Nick Craver

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5 Comments

James South Over a year ago

Hmmm... When I run through this in firebug though I can actually step into my function. I't only when I hit the line if (typeof testString !== "undefined") that it goes boom.

Nick Craver Over a year ago

@James - In that case you have a different issue, where is foo defined in the scope above?

James South Over a year ago

Thats's the essence of my test. I'm tring to cater for a scenario where someone attempts to pass an undefined parameter to the function. Probably overkill i'm sure (I probably shouldn't be hiding errors like that either really)

Nick Craver Over a year ago

@James - There's not much you can do about that...if it's set to undefined that's ok, but if it's literally not defined, it'd going to blow up when you attempt to pass it to any function...not much you can do about it, basics of the language.

James South Over a year ago

Cheers for that. The more I think about it the more I reckon that it would have been overkill if possible anyway..... Accepted.

Felix Kling · Accepted Answer · 2010-12-24 11:53:11Z

0

I get the error too, but it is is not related to your code, it is because you pass a variable that does not exist to a function. This works:

var foo = undefined;
var test = peachUI().stringIsNullOrEmpty(foo) ;

Btw. the error already tells you that the problem is not in your function, otherwise it be 'testString' is undefined.

answered Dec 24, 2010 at 11:53

Felix Kling

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1 Comment

James South Over a year ago

You know I'd have never interpreted the error message that way... cheers!

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