CODEWITHSUNDEEP
javascriptarraysobjectundefined
simplesystems
simplesystems

Reputation: 849

Javascript check if undefined doesnt work

I want to check if a object is defined or not..

content of the Object:

Object

so I'll do:

if (e.model.item.state  != "undefined"){
var stateID = e.model.item.state.id;
....
}
else{

}

Then e.model.item.state is undefined but it does enter the if clause and stops here:

var stateID = e.model.item.state.id;

because of undefined..!

I tried also:

 !== "undefined"
 !=== "undefined"

Upvotes: 0

Views: 141

Answers (4)

Vivek Pratap Singh
Vivek Pratap Singh

Reputation: 9974

Better use this to avoid unnecessary undefined error:-

if (e && e.model && e.model.item & e.model.item.state) {
   // e.model.item.state is NOT `undefined`, `null`, `false` or `0`
}

Upvotes: 3

choz
choz

Reputation: 17858

In JS, you can check whether a variable is either undefined, null, false or 0 by just simply doing,

if (e.model.item.state) {
   // e.model.item.state is NOT `undefined`, `null`, `false` or `0`
}
else {
   // e.model.item.state is either `undefined`, `null`, `false` or `0`
}

Upvotes: 2

Ronen Ness
Ronen Ness

Reputation: 10740

"undefined" is not the same as undefined. The first one is a string with the word 'undefined' in it, the other is a reserved js term for undefined var.

Doing something == "undefined" is comparing it to a string. You should remove the quotes.

Upvotes: 2

Mohit Bhardwaj
Mohit Bhardwaj

Reputation: 10083

You check for undefined in one of following ways:

var a;

if( a === undefined )

OR

if( typeof a === "undefined" )

"undefined" is not equal to undefined. So, if you compare directly for equality, use it without quotes. If you are using typeof operator, you need to use quotes because typeof always returns a string value.

Upvotes: 0

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