Repeat String - Javascript

Question

What is the best or most concise method for returning a string repeated an arbitrary amount of times?

The following is my best shot so far:

function          


        

Answer 1

Use Lodash for Javascript utility functionality, like repeating strings.

Lodash provides nice performance and ECMAScript compatibility.

I highly recommend it for UI development and it works well server side, too.

Here's how to repeat the string "yo" 2 times using Lodash:

> _.repeat('yo', 2)
"yoyo"

Answer 2

This one is pretty efficient

String.prototype.repeat = function(times){
    var result="";
    var pattern=this;
    while (times > 0) {
        if (times&1)
            result+=pattern;
        times>>=1;
        pattern+=pattern;
    }
    return result;
};

Answer 3

Here's a 5-7% improvement on disfated's answer.

Unroll the loop by stopping at count > 1 and perform an additional result += pattnern concat after the loop. This will avoid the loops final previously unused pattern += pattern without having to use an expensive if-check. The final result would look like this:

String.prototype.repeat = function(count) {
    if (count < 1) return '';
    var result = '', pattern = this.valueOf();
    while (count > 1) {
        if (count & 1) result += pattern;
        count >>= 1, pattern += pattern;
    }
    result += pattern;
    return result;
};

And here's disfated's fiddle forked for the unrolled version: http://jsfiddle.net/wsdfg/

Answer 4

Simple method:

String.prototype.repeat = function(num) {
    num = parseInt(num);
    if (num < 0) return '';
    return new Array(num + 1).join(this);
}

Answer 5

function repeat(s, n) { var r=""; for (var a=0;a<n;a++) r+=s; return r;}

Answer 6

function repeat(pattern, count) {
  for (var result = '';;) {
    if (count & 1) {
      result += pattern;
    }
    if (count >>= 1) {
      pattern += pattern;
    } else {
      return result;
    }
  }
}

You can test it at JSFiddle. Benchmarked against the hacky Array.join and mine is, roughly speaking, 10 (Chrome) to 100 (Safari) to 200 (Firefox) times faster (depending on the browser).