detect an undefined item in jQuery

Question

How do you detect an undefined item in jQuery in an 'if statement' I have tried something like below without any success so far.

 success: function(data){

  if(typeof data.DATA[0].RECIPIENTID = 'undefined'){
     // do nothing                          
   }
   else {
       //else get value
       console.log(data.DATA[0].RECIPIENTID);                       
   }


 console.log(data);

 }
});

This is a JavaScript (language) question, not a jQuery (library) one. — Matt Ball, Aug 28 '12 at 14:40

score 9 · Accepted Answer · edited May 23 '17 at 12:33

9

= is an assigment operator in JavaScript. Use ===, not =.

if(typeof data.DATA[0].RECIPIENTID === 'undefined'){
    // ...
}
// ...

See also Which equals operator (== vs ===) should be used in JavaScript comparisons?

edited May 23 '17 at 12:33

Community

1
1

answered Aug 28 '12 at 14:37

Matt Ball

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710

score 1 · Answer 2 · answered Aug 28 '12 at 14:41

1

undefined does not need quotes ''

    if(RECIPIENTID === undefined){
     // do nothing                          
   alert("undefined");
}

answered Aug 28 '12 at 14:41

This_is_me

908
9
20

1

Careful with this one, `undefined` needn't be undefined: `(function(undefined,foo){console.log(foo === undefined); console.log(undefined);})('bar')` paste this in your console – Elias Van Ootegem Aug 28 '12 at 14:48
1

Compare that to: `(function(foo,undefined){console.log(foo === undefined); console.log(undefined);})(undefined,'bar')` and `(function(foo,undefined){console.log(foo === undefined); console.log(undefined);})()` – Elias Van Ootegem Aug 28 '12 at 14:49
I still get TypeError: data.DATA[0] is undefined [Break On This Error] if(data.DATA[0].RECIPIENTID === undefined){ -- any idea why? – Prometheus Aug 28 '12 at 15:03

detect an undefined item in jQuery

2 Answers2