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Old June 14th, 2005, 04:08 AM
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Default How to know a variable is undefined?

How to know if a variable is defined in Javascript? Which function I can use?

Thanks in advance.

Old June 14th, 2005, 06:19 AM
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Alert it by name?

<script language ="javascript">
var 1 = ("1")


The alert should return 1.


Old June 14th, 2005, 06:40 AM
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You can use typeof...
if(typeof myVar == "undefined"){
    // variable is undefined, do something 
However typeof will return "undefined" if a variable has not been set to any value / object / etc., so var myVar; would return "undefined" and var myVar = null; would not.



Old June 14th, 2005, 10:14 AM
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Also, 1 is not a valid variable name; it's a value.

var a1 = ("1")


would work.....


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