Array Join vs String Concat

String concatenation is faster in ECMAScript. Here's a benchmark I created to show you:

http://jsben.ch/#/OJ3vo

From 2011 and into the modern day ...

See the following join rewrite using string concatenation, and how much slower it is than the standard implementation.

// Number of times the standard `join` is faster, by Node.js versions:
// 0.10.44: ~2.0
// 0.11.16: ~4.6
// 0.12.13: ~4.7
// 4.4.4: ~4.66
// 5.11.0: ~4.75
// 6.1.0: Negative ~1.2 (something is wrong with 6.x at the moment)
function join(sep) {
    var res = '';
    if (this.length) {
        res += this[0];
        for (var i = 1; i < this.length; i++) {
            res += sep + this[i];
        }
    }
    return res;
}

The moral is - do not concatenate strings manually, always use the standard join.

I can definitely say that using Array.join() is faster. I've worked on a few pieces of JavaScript code and sped up performance significantly by removing string manipulation in favor of arrays.