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) {
}
3 Answers
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.
3 Comments
LoremIpsum
+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.
rooby
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)
Greg
if (arr.length > 0) is the more readable option. It tells anyone looking at your code that you expect arr to be a variable of a type that has a length property that is a number, and you are not expecting a case where arr.length = '', undefined, NaN, or null. It's more obvious to use this in the general sense, if (myVar.prop > 0), but I have seen code where the case where arr.length is undefined occurs.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){...}
2 Comments
Hanna
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.
zeachco
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.)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) {
}
2 Comments
Mwr247
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.
rooby
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)
if(arr[0])works just fine too.