Javascript: How to check if a string is empty?

Question

I know this is really basic, but I am new to javascript and can't find an answer anywhere.

How can I check if a string is empty?

See http://stackoverflow.com/questions/154059/what-is-the-best-way-to-check-for-an-empty-string-in-javascript — Crescent Fresh, Mar 04 '10 at 17:42
does whitespace count as empty? if so, you'll likely want a regex to test it. — scunliffe, Mar 04 '10 at 17:42
Came here to add that some people should actually be checking for `isBlank` which would be `variable.trim() === ''` — Dennis, May 06 '19 at 00:40
Trimming a string always make sense if(title.trim().length === 0) { //code} — Amitesh Bharti, Jul 24 '19 at 06:20

score 173 · Answer 1 · answered Mar 04 '10 at 17:46

173

I check length.

if (str.length == 0) {
}

answered Mar 04 '10 at 17:46

Dustin Laine

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I'm being a bit pedantic but `if (!str || str.length === 0)` would be preferable. (Note the 3 equals signs.) +1 to @Dustin though. – intrepidis Jun 21 '13 at 14:46
13

If you add blank spaces to your string, `length` counts the blank spaces, so with `length` we can't determine whether a string is empty or not. – avolquez Aug 28 '13 at 12:21
9

@evolquez space is not same as empty, so is the case with null. space is a character so it can't be treated as `""`. OP is asking about empty string and I think this solution works well. – Fr0zenFyr Jul 04 '14 at 04:57
1

@ChrisNash Why would you need `===` instead of `==` in this specific case? Is it possible for `str.length` to return something other than a numeric value that might evaluate to `falsy`? – user Sep 11 '14 at 11:16
@buffer This explains it all: http://stackoverflow.com/questions/359494/does-it-matter-which-equals-operator-vs-i-use-in-javascript-comparisons – intrepidis Sep 11 '14 at 19:57
3

@ChrisNash I understand why `===` is better in general, but for this specific case, I can't find a reason where `str.length` would be zero due to type conversion. Are you using it as a convention or is there an example where you can get unexpected results? – user Sep 12 '14 at 05:05
var str = " "; now how you will check ???? – insCode Sep 08 '16 at 08:10
9

Don't forget to trim `if (!str || str.trim().length === 0)` – Jake Pucan Feb 27 '19 at 07:54
@intrepidis not pedantic at all, that's core, foundational js. You just saved one some unnecessary aggravation. This answer as it stands is small disaster waiting to happen. – MrBoJangles Jul 09 '19 at 16:39
so why `.length == 0` is better than `=== ""` ??? I need an answer. – Vladimir Kovalchuk Apr 28 '21 at 13:58

score 60 · Answer 2 · answered Mar 04 '10 at 17:46

If you want to know if it's an empty string use === instead of ==.

if(variable === "") {
}

This is because === will only return true if the values on both sides are of the same type, in this case a string.

for example: (false == "") will return true, and (false === "") will return false.

score 11 · Answer 3 · answered Mar 04 '10 at 17:42

11

This should work:

if (variable === "") {

}

answered Mar 04 '10 at 17:42

Tom Castle

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score 11 · Answer 4 · edited Apr 16 '19 at 19:07

11

But for a better check:

if(str === null || str === '')
{
    //enter code here
}

edited Apr 16 '19 at 19:07

JeanValjean

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answered Mar 04 '10 at 17:49

Christopher Richa

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Actually I was going to edit this before it got closed: if(!str || str == "") { //enter code here } There are many ways to do this, but a String is not necessarily null if it has "" in it. Empty is **not** null. – Christopher Richa Mar 04 '10 at 18:35
3

where did you learn that a null variable has a length of 0 in JS? What is the source where you found this info? – PositiveGuy Nov 07 '11 at 07:07
1

What if str is undefined? If you're checking falsiness, your best bet is `if (!str)`. But if you're checking for empty string, as per the question, I think nxt's is the best. The accepted answer should be using ===, and if str is null/undefined, you get your classic Uncaught ReferenceError. – MrBoJangles Jul 09 '19 at 16:37
This answer is miscorrect because the condition gonna be truthy even if variable `str` is `null`, while `null` is an `object` type, not `string`. – Nickensoul Aug 19 '20 at 17:04

score -13 · Answer 5 · answered Mar 04 '10 at 17:41

-13

if (value == "") {
  // it is empty
}

answered Mar 04 '10 at 17:41

Ray

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If value is really a string, then this is correct, but it will also return true, if value = false or 0 or null. use === instead. – Residuum Mar 04 '10 at 17:43
2

@Residuum: The question reads “How to check if a string is empty?” – Gumbo Mar 04 '10 at 17:44
3

@Gumbo: An answer that works under all circumstances is in my opinion better than an answer that provides the bare minimum, so I agree with Residuum. Things like that are especially important to point out for a beginner. – OregonGhost Mar 04 '10 at 17:47
2

@Gumbo: As the question suggests, the questioner is not experienced in Javascript. And as Javascript is not a strongly typed language, it is a common source of error to not explicitly check for type as well. Been there, done that. – Residuum Mar 04 '10 at 17:48

Javascript: How to check if a string is empty?

5 Answers5