Generating strings with # number of characters

Question

Is there way of generating a string made up of 250 underscores, without using a loop? I want to avoid writing code like this:

var myString= '';
for (var i=0; i < 250; i++) {
    myString += '_';
}

possible duplicate of [Repeat String - Javascript](http://stackoverflow.com/questions/202605/repeat-string-javascript) — Felix Kling, Jun 02 '13 at 17:57

score 8 · Accepted Answer · edited May 23 '17 at 10:09

8

There's no built-in solution but the question Repeat String - Javascript has a nice solution:

If you don't want to alter the String prototype you can just do:

var num = 250;
var myChar = '_';
var myString = new Array(num + 1).join(myChar);

This is creating an array of 251 undefineds an then joining them by your character. Since undefined is '' (empty string) when converted to a string in .join(), this gives you the string you're after.

edited May 23 '17 at 10:09

Community

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answered Sep 22 '09 at 09:17

Greg

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actually, `undefined` converted to string is `"undefined"` and not the empty string; that `undefined` and `null` entries of the arry will be converted to `""` is particular to `join()` – Christoph Sep 22 '09 at 10:26
Wow, this is probably one of the most convoluted ways to create a string that only contains a single repeating character. – Bombe Sep 22 '09 at 11:21
@Bombe: using arrays as string builders isn't uncommon, so it's not really that far fetched... – Christoph Sep 22 '09 at 11:30

score 2 · Answer 2 · answered Sep 22 '09 at 09:22

2

Its a bit of a hack, but you could do something like:

var arr = new Array(251);
var lineStr = arr.toString().replace(/,/g, "_");

answered Sep 22 '09 at 09:22

James

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score 1 · Answer 3 · answered Sep 22 '09 at 09:18

1

Use a constant that is longer that the longest number of underscores and use substring() to get as many as you need.

answered Sep 22 '09 at 09:18

Aaron Digulla

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score 0 · Answer 4 · answered Sep 22 '09 at 09:12

0

var myString = "__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________";

Why do you want to generate it? And why do you want to avoid a for loop?

answered Sep 22 '09 at 09:12

Bombe

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Because the string size can vary on different occasions. I was sure there was an easier approach, something like: var myString = new char('_', 250); or something similar? – Andy Sep 22 '09 at 09:14
Write a method that accepts the string size n and returns a string of n underscores. Because a for loop is the most straight forward and AFAIK, the fastest way to do this. – Amarghosh Sep 22 '09 at 09:39

score 0 · Answer 5 · edited May 23 '17 at 12:10

Here's a function which creates the string in (more or less) logarithmic runtime:

function repeat(string, times) {
    if(!(times = +times)) return ''; // convert to number; check for NaN, 0
    var result = '' + string, i = 1;
    for(; i * 2 <= times; i *= 2) result += result;
    for(; i < times; ++i) result += string;
    return result;
}

var u250 = repeat('_', 250);

Hopefully, I didn't mess up the loop conditions ;)

Also, Aaron's suggestion can be automated:

function underscores(count) {
    while(count > underscores.buffer.length)
        underscores.buffer += underscores.buffer;
    return underscores.buffer.substring(0, count);
}
underscores.buffer = '_';

var u250 = underscores(250);

Generating strings with # number of characters

5 Answers5