Is an empty array always interpreted as TRUE?

Question

Is this the case in all browser versions? Meaning, an empty array is always considered as TRUE and never as FALSE as a boolean representation?

var x = [];

if(x)
   alert('this could be an empty array');
else
    alert('this could NEVER be an empty array');

Yes it is. That's why you'd use something like isempty/isset or count to see if it's empty or not — user3036342, Apr 09 '14 at 12:24

score 3 · Accepted Answer · edited May 23 '17 at 12:01

According to ECMA Script 5.1 specification's Boolean expression evaluation function, any object will be always evaluated to be Truthy. So, an array will be always evaluated to be truthy.

+-----------------------------------------------------------------------+
| Argument Type | Result                                                |
|:--------------|------------------------------------------------------:|
| Undefined     | false                                                 |
|---------------|-------------------------------------------------------|
| Null          | false                                                 |
|---------------|-------------------------------------------------------|
| Boolean       | The result equals the input argument (no conversion). |
|---------------|-------------------------------------------------------|
| Number        | The result is false if the argument is +0, −0, or NaN;|
|               | otherwise the result is true.                         |
|---------------|-------------------------------------------------------|
| String        | The result is false if the argument is the empty      |
|               | String (its length is zero); otherwise the result is  |
|               | true.                                                 |
|---------------|-------------------------------------------------------|
| Object        | true                                                  |
+-----------------------------------------------------------------------+

As per the last line, for any Object, result will be true.

Reference: My answer to the other question in SO

score 1 · Answer 2 · answered Apr 09 '14 at 12:25

1

Arrays are truthy, yes. If you want an easy way to check for emptiness, use the length property:

var x = [];

if(x.length)
    alert('this array is not empty');

answered Apr 09 '14 at 12:25

Platinum Azure

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score 0 · Answer 3 · answered Apr 09 '14 at 12:23

0

Yes. All objects are truthy. Always.

answered Apr 09 '14 at 12:23

Niet the Dark Absol

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score 0 · Answer 4 · answered Apr 09 '14 at 12:24

0

Yes. Array is an object. So it is true. whereas, null/undefined is false

answered Apr 09 '14 at 12:24

vivek_nk

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score 0 · Answer 5 · answered Apr 09 '14 at 12:26

0

by default these are things are treated as false in javascript.

false
null
undefined
'' or "" [empty string]
0 [zero]

answered Apr 09 '14 at 12:26

Pushker Yadav

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"By default"? If you're going to say things like that, you should also at least give a cursory mention of when that behavior does not apply. (Though I can't think of any circumstances where the above is not true.) – Platinum Azure Apr 09 '14 at 12:29
simple, you using other than these then result will be true. – Pushker Yadav Apr 09 '14 at 12:34

Is an empty array always interpreted as TRUE?

5 Answers5