Array Join vs String Concat

Question

Which method is faster?

Array Join:

var str_to_split = "a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z";
var myarray = str_to_split.split(",");

var output=myarray.join("");

---

String Concat:

var str_to_split = "a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z";
var myarray = str_to_split.split(",");

var output = "";
for (var i = 0, len = myarray.length; i<len; i++){
    output += myarray[i];
}

Answer 1

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.

Answer 2

The spread operator, written with three consecutive dots ( ... ), is new in ES6 and gives you the ability to expand, or spread, iterable objects into multiple elements.

const books = ["Don Quixote", "The Hobbit", "Alice in Wonderland", "Tale of Two Cities"];
console.log(...books);

Prints: Don Quixote The Hobbit Alice in Wonderland Tale of Two Cities

Answer 3

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.

Answer 4

Manual concatenation is faster, for a numeric array of fixed length.

Here's a JSPerf test that tests these two operations:

zxy.join('/')

// versus

zxy[0] + '/' + zxy[1] + '/' + zxy[2]

// given the array

zxy = [1, 2, 3]

// resulting in the string '0/1/2'

Results: Using Chrome 64.0.3282.186, Array.join was 46% slower.

Answer 5

According to this Google document titled 'Optimizing JavaScript code' string concat is slower then array join but apparently this is not true for modern Javascript engines.

I made a benchmark for the Fibonacci test example that they used in the document and it shows that concatenating (gluing) the string is almost 4x as fast as using Array join.

Answer 6

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

http://jsben.ch/#/OJ3vo