array.length vs. array.length > 0

Question

Is there any difference between checking an array's length as a truthy value vs checking that it's > 0?

In other words is there any reason to use one of these statements over the other:

var arr = [1,2,3];
if (arr.length) {
}

if (arr.length > 0) {
}

if you know it's an array of objects (like a dom query result lib call), `if(arr[0])` works just fine too. — dandavis, Oct 02 '15 at 16:16

score 23 · Answer 1 · answered Oct 02 '15 at 16:13

23

Is there any difference between checking an array's length as a truthy value vs checking that it's > 0?

Since the value of arr.length can only be 0 or larger and since 0 is the only number that evaluates to false, there is no difference.

In general, Boolean(n) and Boolean(n > 0) yield different results for n < 0.

In other words is there any reason to use one of these statements over the other

Only reasons related to code readability and understanding, not behavior.

answered Oct 02 '15 at 16:13

Felix Kling

2

+1 for that last sentence. You can do pretty much anything with JavaScript, even if it's stupid or hard to read. It takes a good developer to write readable code. – LoremIpsum Oct 02 '15 at 16:57
2

It's also debatable which of those is the more readable option. IMO it is `if (array.length)` but I know other people who prefer `if (array.length > 0) – rooby Jul 07 '20 at 01:17

score 15 · Accepted Answer · edited Feb 11 '19 at 18:25

15

array.length is fastest and shorter than array.length > 0. You can see difference of their speeds : http://jsperf.com/test-of-array-length

if(array.length){...} is similar to if(0){...} or if(false){...}

edited Feb 11 '19 at 18:25

jbyrd

answered Oct 02 '15 at 16:41

Sherali Turdiyev

Interestingly enough `array.length` ran slower for me than `array.length > 0` in Chrome 59. Not sure how that's possible since intuitively it seems like it would be doing less. – Hanna Jul 11 '17 at 12:41
1

Chrome VM optimises in different ways each new version. If you have to think what the compiler is doing behind, knowing V8 is written in C++ and C++ is typed, the array length which is a number is treated as a boolean expression so I would say that in some cases it does the equivalent of `Boolean(array.length)` when the `> 0` is not present. There are a lots of different values that can be true or false in javascript and they all require a check (null, false, undefined, 0, '', etc.) – zeachco Mar 29 '21 at 15:52

score 11 · Answer 3 · edited May 23 '17 at 12:02

11

In javascript, they dont make a difference.

In the end, whatever is in between the if parenthesis will evaluate to a truthy or falsey value

For all possible falsey values, see All falsey values in JavaScript

If you wish to be more clear and explicit, use

if (arr.length > 0) {
}

If you wish to be less verbose, use

if (arr.length) {
}

edited May 23 '17 at 12:02

Community

answered Oct 02 '15 at 16:13

AmmarCSE

5

To add emphasis to this answer, many developers choose clarity over being concise. It helps with code readability when scanning over it. Otherwise, there is no difference. – Mwr247 Oct 02 '15 at 16:16
More explicit yes. More clear though is debatable. In some cases, like this one, I think clarity is relatively equal with either option. Often I would go for the more verbose option but in this case I don't think it adds any value. I read it as "if the array has length", which is perfectly understandable IMO so I don't think the > 0 adds value. I think it actually just adds unnecessary noise, although maybe I've adapted to that over years of reading it without the > 0 so I can see how it would be easier that way for someone not used to it. (See, I'm usually pro verbosity :D) – rooby Jul 07 '20 at 01:24

3 Answers3