Better way to see if an object is present in JavaScript

Question

Is

if(!!object)
{
 // do something if object found
}

a much more guarenteed way to see if any object is present?

if(object)
{

}

possible duplicate of [How can I check whether a variable is defined in JavaScript?](http://stackoverflow.com/questions/519145/how-can-i-check-whether-a-variable-is-defined-in-javascript) — Felix Kling, May 24 '12 at 14:14

score 7 · Answer 1 · answered May 24 '12 at 14:10

7

the safest way to check that something is defined:

if (typeof thingy !== 'undefined')

answered May 24 '12 at 14:10

jbabey

45,965
12
71
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1

why wouldn't !thingy catch this case? – unj2 May 24 '12 at 14:20
@kunj2aan Consider the different outcome when dealing with a variable containing the value `false` or any falsy value. If you can make some assumption about your variable then other methods are fine. For instance, the result of `getElementById` will often just use `if(result)` because you know it will never return false or 0. – James Montagne May 24 '12 at 14:35
@kunj2aan `!thingy` will throw an exception if thingy has not been defined. – jbabey May 24 '12 at 14:49

score 1 · Answer 2 · answered May 24 '12 at 14:14

1

if(typeof my_var == 'object'){

}

answered May 24 '12 at 14:14

Rycicle

11
2

score 1 · Answer 3 · answered May 24 '12 at 14:21

1

There are so many ways to check that...

if ( object )
if ( !!object )
if ( object !== undefined )
if ( typeof object !== 'undefined' )
if ( object !== void 0 )
if ( {}.toString.apply( object ).subtr( 0, 7 ) === '[object' )

Etc.

answered May 24 '12 at 14:21

Florian Margaine

58,730
15
91
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Better way to see if an object is present in JavaScript

3 Answers3