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Easy questions about if() and getElementById

P: 3
Please forgive my ignorance. I've read a lot of reference and instructional materials but I need a couple of basic things clarified.

Suppose, in JavaScript, I do like so:

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  1. var a,b;
  2. a=document.getElementById("element");
  3. if(a){b= // . . . et cetera
I have seen people do things like this. My two questions:

1. What exactly does the variable a get filled with in line 2? It supposedly becomes a "reference" to the object with the specified ID, but what form does this "reference" take, specifically?

2. What's the purpose of the if() statement in the third line?

Thank you.
Dec 18 '08 #1
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1 Reply


Dormilich
Expert Mod 5K+
P: 8,639
1. a holds an object (which in this case is an HTMLElement object)
2. the if statement checks whether the allocation of line 2 was successful, that is if a holds the element object or not (ie. there was no element having an id="element")

if (a) is true for any value of a besides null, 0, false and '' (empty string)

regards

note: try this:
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  1. alert(a);
Dec 18 '08 #2

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