Checking for an empty string array

Question

I'm trying to check for an empty string array like this:

var array = ['',''];
//Other code
if (array == ['',''])
    //Do stuff

and I've found that

['',''] == ['','']

returns false. Why is that? What method should I use to check for an empty string array? Is there a way where I don't have to check each individual item?

Possible duplicate of [How can I check JavaScript arrays for empty strings?](http://stackoverflow.com/questions/3457807/how-can-i-check-javascript-arrays-for-empty-strings) — Sterling Archer, Apr 27 '17 at 17:08
Are you checking for a single element having empty string as value? — guest271314, Apr 27 '17 at 17:09
@NinaScholz The empty array I'm comparing against is always constant. Basically, I want to see if `array` contains only empty strings — derekantrican, Apr 27 '17 at 17:19
@guest271314 I would like to check the whole array at once (if this is possible in JavaScript) rather than creating another loop to check each item, one at a time — derekantrican, Apr 27 '17 at 17:20
@MikeMcCaughan I'm using Google Apps Script and I don't believe I can use LINQ there — derekantrican, Apr 27 '17 at 17:22
It's not LINQ, it's JavaScript (technically, ECMAScript 2015). — Heretic Monkey, Apr 27 '17 at 17:23
@MikeMcCaughan Well, it throws an error in Google Apps Script: http://i.imgur.com/ZpKdbQQ.png — derekantrican, Apr 27 '17 at 17:26
@derekantrican Umm, how can you check if every element is an empty string without checking every element, one way or another? — , Apr 27 '17 at 17:27
Oh, DumbScript, sorry. `!array.every(function (item) { return item.length; });` — Heretic Monkey, Apr 27 '17 at 17:31

Nina Scholz · Accepted Answer · 2017-04-27T17:42:37.857

4

Beside the proposed using of Array#toString method, I suggest to use Array#join with an empty string as separator and then test the result. The advantage is, it works for an arbitrary count of elements inside of the array.

var bool = array.join('') ? 'not all empty string' : 'all empty string';

edited Apr 27 '17 at 17:42

answered Apr 27 '17 at 17:41

Nina Scholz

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Nice one. Hadn't thought of using `join`. – Pedro Castilho Apr 27 '17 at 17:42

Pedro Castilho · Answer 2 · 2017-04-27T17:36:18.850

['', ''] == ['', ''] returns false because in JavaScript arrays are objects, and objects in JavaScript have reference semantics. Comparing objects to each other actually compares their reference IDs, which will be different for different references. So, even though both sides of == are the "same" array, they are different references.

If you want to check that an array only contains empty strings, use Array.prototype.every as in the following:

myArray = ['']
console.log(myArray.every(el => el === '')) // true
myArray = []
console.log(myArray.every(el => el === '')) // true
myArray = ['test']
console.log(myArray.every(el => el === '')) // false

If you are in an environment without ES6 support, you can swap the el => el === '' for function(el) { return el === '' }.

I am using Google Apps Script and this doesn't seem to work there: http://i.imgur.com/CLteUor.png — derekantrican, Apr 27 '17 at 17:28

score 0 · Answer 3 · answered Apr 27 '17 at 17:32

0

You can do this:

var arr = ["","", ""].reduce(function (a, b) {
  return a + b;
});

if(arr == "") {
console.log('Array is empty');
}

answered Apr 27 '17 at 17:32

Pankaj Shukla

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Your `reduce` is just a clumsy way to write `join`. Your code also won't work if the input array has no elements. – Apr 27 '17 at 17:33
@torazaburo Point taken but the OP, didn't talk about empty array,, in the sense that array has no elements. What is your suggestion to make it better? – Pankaj Shukla Apr 27 '17 at 17:39
`var arr = ["", "", ""].join('');`. – Apr 27 '17 at 18:06
My idea was towards reducing the array to single element,which what join() is doing here. Also, there are some studies that have been done that suggest that in modern browsers string concatenation is much faster than join() method. Hence I chose reduce(), which is doing string concatenation. These threads have such discussions: http://stackoverflow.com/questions/7299010/why-is-string-concatenation-faster-than-array-join Another one, not exactly same but similar from Kyle Simpson, not so long ago https://davidwalsh.name/combining-js-arrays – Pankaj Shukla Apr 27 '17 at 18:11

score 0 · Answer 4 · edited Nov 23 '19 at 20:07

0

This should also work:

var arr = [""];
console.log(String.valueOf(arr[0]) === String.valueOf(''));

edited Nov 23 '19 at 20:07

lczapski

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answered Nov 23 '19 at 18:30

user12421871

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score 0 · Answer 5 · answered Aug 08 '20 at 13:23

0

Based on the answer from Nina above this should also work!

 let arr1 = ['']
 const bool1 = !!arr1.join(''); // false
 console.log(bool1)
            
 let arr2 = ['String']
 const bool2 = !!arr2.join(''); // true
 console.log(bool2)

answered Aug 08 '20 at 13:23

Marko Barleben

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Checking for an empty string array

5 Answers5

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