How to easily check if undefined in javascript object?

Question

Assuming I have a javascript object "myobject" that just contains an empty object "{}".

I ideally in my code I want to do the following:

if (theobject[keyvar][subkeyvar]) {
  // do something
}

The issue now is that because keyvar and subkeyvar do not actually exist within the object, it fails and comains that the properties are undefined. What is the simplest/least lines of code/best way to be able to do have it just "know it is undefined" and continue to execute the //do something or not without crashing?

I dont want to get too carried away with checking like:

if( keyvar in theobject ) {
   if(subkeyvar in theobject) {
        if.....
   }
}

If they both can possibly be undefined, you have to test one, then the other. — user400654
– user400654, Commented Mar 7, 2014 at 17:01
but note that those tests don't just check for undefined but also for 0, null, NaN, false and "". — Denys Séguret
– Denys Séguret, Commented Mar 7, 2014 at 17:03
If you're checking for existence, use in. If you're checking for a value, use === — Ian
– Ian, Commented Mar 7, 2014 at 17:16

Yusaf Khaliq · Accepted Answer · 2014-03-07 17:30:36Z

1

if (typeof theobject[keyvar] !== "undefined" && typeof theobject[keyvar][subkeyvar] !== "undefined") {
  // keyvar and subkeyvar defined

}

first we check if keyvar typeof is undefined and then if subkeyvar is undefined and if they are both defined typeof theobject[keyvar] !== "undefined" && typeof theobject[keyvar][subkeyvar] !== "undefined" is true.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/typeof

edited Mar 7, 2014 at 17:30

answered Mar 7, 2014 at 17:04

Yusaf Khaliq

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1 Comment

DontVoteMeDown Over a year ago

Please add an explanation.

Amir Sherafatian · Accepted Answer · 2014-03-07 17:04:25Z

0

you can try this :

if (theobject[keyvar] && theobject[keyvar][subkeyvar]) {

    // do something
}

answered Mar 7, 2014 at 17:04

Amir Sherafatian

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Comments

user400654 · Accepted Answer · 2014-03-07 17:12:29Z

0

If they both can possibly be undefined, you have to test one, then the other.

if (theobject[keyvar] && theobject[keyvar][subkeyvar]) {

This will of course fail on a key containing 0 or "" (or several other falsey but not undefined values) so you may want to use typeof on the second test.

edited Mar 7, 2014 at 17:12

answered Mar 7, 2014 at 17:03

user400654

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Comments

tewathia · Accepted Answer · 2014-03-07 17:13:28Z

0

Try:

if (theobject[keyvar] !== undefined && theobject[keyvar][subkeyvar] !== undefined) {
    // do something
}

Since the && operator is used, the if will not check the second value if the first value is falsey, so you will never get the 'properties are undefined` error

edited Mar 7, 2014 at 17:13

answered Mar 7, 2014 at 17:05

tewathia

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Comments

ohmu · Accepted Answer · 2014-03-07 17:21:33Z

0

theObject.hasOwnProperty(keyvar) && theObject.hasOwnProperty[keyvar].hasOwnProperty(subkeyvar)

edited Mar 7, 2014 at 17:21

ohmu

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answered Mar 7, 2014 at 17:04

madhured

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1 Comment

Johan Over a year ago

What if the property is defined in the prototype chain?

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