Checking if variable exists in javascript doesn;t work

Question

Tried:

var xxx = (typeof my_var.property !== 'undefined') ? my_var.property : 'fu';

I get:

Uncaught exception: ReferenceError: Undefined variable: my_var

well I know it's undefined, but why do I get that error?? xxx should take the fu value...

Joachim Sauer · Accepted Answer · 2011-11-22 14:25:55Z

5

Your code checks if the type of my_var.property is undefined. But that can't be checked because the type of my_var itself is already undefined.

answered Nov 22, 2011 at 14:25

Joachim Sauer

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Comments

Martin. · Accepted Answer · 2011-11-22 14:26:30Z

3

Try to check only my_var first, it can be undefined, too

var xxx = (typeof my_var !== 'undefined' && my_var.property !== 'undefined') ? my_var.property : 'fu';

answered Nov 22, 2011 at 14:26

Martin.

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Comments

solendil · Accepted Answer · 2011-11-22 14:26:20Z

2

Evaluation of my_var.property fails because my_var is null or undefined. Enhance your code like this:

var xxx = (my_var && typeof my_var.property !== 'undefined') ? my_var.property : 'fu';

answered Nov 22, 2011 at 14:26

solendil

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Comments

Prashant Bhate · Accepted Answer · 2011-11-22 14:27:02Z

2

Add another check for my_var

var xxx =  (typeof my_var != 'undefined' && typeof my_var.property !== 'undefined')? my_var.property : 'fu';

answered Nov 22, 2011 at 14:27

Prashant Bhate

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Comments

Murtaza · Accepted Answer · 2011-11-22 14:30:05Z

1

i think you should first check for my_var

if(!myvar) 
{
     var xxx = (typeof my_var.property !== 'undefined') ? my_var.property : 'fu';
     alert(xxx);
}

answered Nov 22, 2011 at 14:30

Murtaza

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