Check if object exists in JavaScript

Question

How do I verify the existence of an object in JavaScript?

The following works:

if (!null)
   alert(\"GOT HERE\");

But this throws a

Answer 1

If you care about its existence only ( has it been declared ? ), the approved answer is enough :

if (typeof maybeObject != "undefined") {
   alert("GOT THERE");
}

If you care about it having an actual value, you should add:

if (typeof maybeObject != "undefined" && maybeObject != null ) {
   alert("GOT THERE");
}

As typeof( null ) == "object"

e.g. bar = { x: 1, y: 2, z: null}

typeof( bar.z ) == "object" 
typeof( bar.not_present ) == "undefined" 

this way you check that it's neither null or undefined, and since typeof does not error if value does not exist plus && short circuits, you will never get a run-time error.

Personally, I'd suggest adding a helper fn somewhere (and let's not trust typeof() ):

function exists(data){
   data !== null && data !== undefined
}

if( exists( maybeObject ) ){
    alert("Got here!"); 
}