Creating array of empty strings?

Question

Is there an easy way to create an array of empty strings in javascript? Currently the only way I can think to do it is with a loop:

var empty = new Array(someLength);
for(var i=0;i<empty.length;i++){
    empty[i] = '';
}

but I'm wondering if there is some way to do this in one line using either regular javascript or coffeescript.

Benjamin Gruenbaum · Accepted Answer · 2017-08-03T11:59:02.370

65

Update: on newer browsers - use .fill: Array(1000).fill('') will create an array of 1000 empty strings.

Yes, there is a way:

 var n = 1000;
 Array(n).join(".").split("."); // now contains n empty strings.

I'd probably use the loop though, it conveys intent clearer.

function repeat(num,whatTo){
    var arr = [];
    for(var i=0;i<num;i++){
        arr.push(whatTo);
    }
    return arr;
}

That way, it's perfectly clear what's being done and you can reuse it.

edited Aug 03 '17 at 11:59

answered Nov 15 '13 at 17:53

Benjamin Gruenbaum

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+1 for cleverness and for mentioning that using the loop makes the intent clear. – Vivin Paliath Nov 15 '13 at 17:54
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This is a cool idea :-) That second function looks familiar ;-) – qwertynl Nov 15 '13 at 17:54
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*(Quietly waits for someone to pick up on the by one index offset)* – Benjamin Gruenbaum Nov 15 '13 at 17:57
1

I think you meant `Array(n).join('.').split('.')` also :) – nderscore Nov 15 '13 at 17:57
`split('.')` fixed the off-by-one error with the original `split('')` – joeytwiddle Apr 07 '16 at 07:18
This created a very nice array of empty strings for me, but still not getting the push values recognized. `// Initialize empty array of strings let faceIds = Array(faces.length).join(".").split(".") for (let face of faces) { faceIds.push(face.faceId) console.log(face.faceId) } return facesIds;` It crashes and says `faceIds` are undefined. – Azurespot Oct 08 '19 at 00:32

score 16 · Answer 2 · edited May 12 '21 at 12:22

16

You can get an array defining the size and fill it with some tokens:

const arr = Array(size).fill("");

edited May 12 '21 at 12:22

Mir-Ismaili

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answered Mar 01 '18 at 14:47

user2592256

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Welcome to StackOverflow: if you post code, XML or data samples, please highlight those lines in the text editor and click on the "code samples" button ( { } ) on the editor toolbar or using Ctrl+K on your keyboard to nicely format and syntax highlight it! – WhatsThePoint Mar 01 '18 at 15:08
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What does this answer add that wasn't already better expressed in the accepted answer? – Mogsdad Mar 01 '18 at 19:20
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@Mogsdad The intent is way clearer and it's more readable. Best answer IMHO. – dan-klasson Dec 12 '18 at 23:02
PS: This returns `any[]` not `string[]` – Darvesh Feb 15 '21 at 06:27

dandavis · Answer 3 · 2016-04-07T20:04:05.680

13

here's a simpler way using generic protos on Array and String:

"".split.call(Array(1001), ",")

EDIT: There's now even simpler ways, some of which are readable:

Array(1000).fill("");

" ".repeat(999).split(" ");

edited Apr 07 '16 at 20:04

answered Nov 15 '13 at 18:59

dandavis

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(Produces 1001 empty strings.) – joeytwiddle Apr 07 '16 at 07:07

score 3 · Answer 4 · answered Jul 27 '18 at 08:16

3

You can try to do it by this way:

let n = 1000;
var emptyStrings = [...Array(n)].map(() => '')

answered Jul 27 '18 at 08:16

Vlad Hilko

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score 3 · Answer 5 · answered Nov 08 '19 at 11:56

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Using Array.from;

const n = 5;
const arr = Array.from({length: n}).map(el => "")
console.log(arr)

answered Nov 08 '19 at 11:56

Sahin Erbay

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This is the shortest answer I was looking for. Thanks @Sahin. – Mo1 Oct 10 '20 at 15:44

score 0 · Answer 6 · answered Nov 15 '13 at 17:54

0

You could make a function out of it:

function stringArray(length) {
    var arr = [];
    for(var i = 0; i < length; ++i) { arr.push(''); }
    return arr;
}

answered Nov 15 '13 at 17:54

qwertynl

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score 0 · Answer 7 · answered Nov 15 '13 at 17:54

0

You could do something like this:

var someLength = 10;
var empty = Array.apply(0, Array(someLength)).map(function(){return '';});
// result: ["", "", "", "", "", "", "", "", "", ""]

answered Nov 15 '13 at 17:54

nderscore

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In case anyone wonders how it works http://stackoverflow.com/questions/18947892/creating-range-in-javascript-strange-syntax :) – Benjamin Gruenbaum Nov 15 '13 at 17:55

score 0 · Answer 8 · answered Nov 15 '13 at 17:59

0

Just for fun

var empty = Array.apply(null, new Array(someLength)).map(String.prototype.valueOf,"");

answered Nov 15 '13 at 17:59

epascarello

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+1 for clever trick with `valueOf`. Side note - new is redundant here. – Benjamin Gruenbaum Nov 15 '13 at 18:07
A bit shorter: `String(Array([length])).split(',').map(String.prototype.valueOf,'')` – KooiInc Nov 15 '13 at 18:15

score 0 · Answer 9 · answered Nov 15 '13 at 18:27

0

The easiest thing to do in CoffeeScript is to use a loop comprehension:

a = ('' for i in [0 ... someLength]) # Note: 3 dots
a = ('' for i in [1  .. someLength]) # Or 2 dots and start at 1
#...

Demo: http://jsfiddle.net/ambiguous/b9Vj9/

answered Nov 15 '13 at 18:27

mu is too short

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Save three chars with some golfing ;-) `[1..5].map(-> '')` – joeytwiddle Apr 07 '16 at 07:12

score 0 · Answer 10 · answered Nov 16 '13 at 17:45

0

Although not widely available, once browsers start supporting EcmaScript 6 array comprehensions, you will be able to do something along the lines of:

var n = 1000;
var empty_strs = ['' for (x of new Array(n))]

answered Nov 16 '13 at 17:45

rdodev

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These are no longer part of ECMAScript 6. (Considered for ES7) – Benjamin Gruenbaum Jan 22 '15 at 17:20

Creating array of empty strings?

10 Answers10