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

I've tested the performance of all the proposed approaches.

Here is the fastest variant I've got.

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;
    }
    return result + pattern;
};

Or as stand-alone function:

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

It is based on artistoex algorithm. It is really fast. And the bigger the count, the faster it goes compared with the traditional new Array(count + 1).join(string) approach.

I've only changed 2 things:

1. replaced pattern = this with pattern = this.valueOf() (clears one obvious type conversion);
2. added if (count < 1) check from prototypejs to the top of function to exclude unnecessary actions in that case.
3. applied optimisation from Dennis answer (5-7% speed up)

UPD

Created a little performance-testing playground here for those who interested.

variable count ~ 0 .. 100:

constant count = 1024:

Use it and make it even faster if you can :)