Having trouble with undefined !== undefined

Question

I'm trying to process a complete function in an ajax call. If the value is undefined, I want cast a var as an empty string. Otherwise, I would like to capture the value into a string array.

The problem is I'm entering the if statement, even when logging the value of the variable in question returns as undefined. What am I missing here?

completefunc: function (xData, Status) {
      $(xData.responseXML).SPFilterNode("z:row").each(function() {
        if(typeof $(this).attr("ows_Products") !== undefined) {
          console.log($(this).attr("ows_Products"));
          arr = $(this).attr("ows_Products").split(',');
        }
        else {
          arr = "";
        }
      });
    }

Have a look at this previous question : http://stackoverflow.com/questions/776950/javascript-undefined-undefined — web_bod, May 14 '12 at 16:47
@web_bod that looked to be more in terms of comparing == to ===, meaning null == undefined = true, whereas null === undefined = false — Wesley, May 14 '12 at 16:50

score 16 · Accepted Answer · answered May 14 '12 at 16:44

16

typeof returns a string value, so you'll need to compare with "undefined" as a string. E.g.,

if(typeof $(this).attr("ows_Products") !== "undefined") { ... }

Edit - more info:

If you check out the MDN page for typeof, you'll see this:

The typeof operator returns a string indicating the type of the unevaluated operand.

This is very different from returning the Type itself (which in JavaScript would probably be something like returning a constructor function like String, Array, etc.). Therefore, when using typeof, you'll always be comparing to strings like "object", "string", "undefined", etc.

answered May 14 '12 at 16:44

jmar777

38,796
11
66
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Ahh yes. It's the little things, sometimes. – Wesley May 14 '12 at 16:46
5

The simplicity of the solution is generally inversely proportionate to how long you spent staring at the problem :) – jmar777 May 14 '12 at 16:49
Ha, thanks. I honestly have to give my dad (also a programmer with far more years of experience) credit for that statement. – jmar777 May 14 '12 at 17:18

score 0 · Answer 2 · answered May 14 '12 at 16:59

0

if($(this).attr("own_Products")){
       arr = $(this).attr("ows_Products").split(',');
}else{
       arr=""
}

answered May 14 '12 at 16:59

kannanrbk

6,964
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Having trouble with undefined !== undefined

2 Answers2