Checking if a node exists in an array

Question

I'm trying to check if a node exists in an array but can't seem to get my if statement correct.

I've currently got :

if (obj2["spec"]["3"]["spec2"]["14"] != null) { do stuff }

In some cases [14] wont exist as the array length is only 5 or 6, so want to make sure it doesn't try to do anything if [14] doesn't have any items in it.

sorry that's my poor typing on here, i've got that in the code. — NewToCode, Dec 22 '16 at 16:54
check this with `undefined` like this `if (obj2["spec"]["3"]["spec2"]["14"] != undefined) { do stuff }` may be that can help you. — Shubham Baranwal, Dec 22 '16 at 17:16

Rafael Dantas · Answer 1 · 2016-12-22T17:43:26.457

-2

You snippet is correct, when a node doesn't exist, is undefined, but in no-strict comparation, undefined == null. If a node doesn't exist, will show a error. if you use typeof, this will cover if all nodes is valid.

Example

// ["spec2"] is undefined, this case will show a error.
if(array["spec"]["3"]["spec2"]["14"] != undefined) { 

}

// This doesn't he show error, if "specs2" is undefined.
if(typeof array["spec"]["3"]["spec2"]["14"] !== "undefined") { 

}

edited Dec 22 '16 at 17:43

answered Dec 22 '16 at 16:55

Rafael Dantas

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`typeof` can never return `undefined`. It may return the *string* `"undefined"`... – lonesomeday Dec 22 '16 at 16:57
@lonesomeday Sorry, I forgot the quotation marks. I corrected – Rafael Dantas Dec 22 '16 at 17:00
OP's `!= null` already ensures it's not undefined. What does your answer attempt to fix? – Oriol Dec 22 '16 at 17:02

score -2 · Answer 2 · edited May 23 '17 at 11:59

-2

If the array length is only 5 or 6, then it means element 14 won't even exist, you should be checking for undefined not null:

if(typeof array["spec"]["3"]["spec2"]["14"] !== "undefined")

or:

if(array["spec"]["3"]["spec2"]["14"] !== undefined)

or even:

if(!array["spec"]["3"]["spec2"]["14"])

I would recommend an option but it really comes down to preference and I'd rather not incite a style/best practice war :) Just pick whichever you prefer.

Here's a thorough explanation on the difference between null and undefined, but essentially null means the value is null, whereas undefined means the variable has not been declared.

edited May 23 '17 at 11:59

Community

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answered Dec 22 '16 at 16:56

Pabs123

3,385
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Or even `!= null`, which is what OP is doing. What does your answer attempt to fix? – Oriol Dec 22 '16 at 17:00
`!= null` is wrong. If you try to access an element in an array which has not been defined yet, it will be undefined not null. try defining an empty array and checking if `arr['something'] == null`, you'll see it returns false – Pabs123 Dec 22 '16 at 17:02
But `undefined == null`. It's an abstract comparison, not strict. – Oriol Dec 22 '16 at 17:02

Checking if a node exists in an array

2 Answers2