Advanced JavaScript Array Concatenation - Performance

Question

I'm trying out two different ways of joining two arrays and using huge arrays to judge their performances but I'm getting an error on the second option and I don't understand why.

I first filled both with 10,000,000 elements with values equal to their index.

var arr1 = [];
var arr2 = [];
for (var i = 0; i < 10000000; i++) {
    arr1[i] = i;
} 
for (var i = 0; i < 10000000; i++) {
    arr2[i] = i;
}

Then:

Option 1 completes fine in ~520ms:

var newArr = arr1.concat(arr2);

Option 2 though throws the following error:

Array.prototype.push.apply(arr1, arr2);

Error:

/private/var/folders/j6/3fs5_k3n17z_0j2xrwj6sphw0000gn/T/CodeRunner/Untitled 9.js:12
Array.prototype.push.apply(arr1, arr2);
                     ^

RangeError: Maximum call stack size exceeded
    at Object.<anonymous> (/private/var/folders/j6/3fs5_k3n17z_0j2xrwj6sphw0000gn/T/CodeRunner/Untitled 9.js:12:22)
    at Module._compile (module.js:435:26)
    at Object.Module._extensions..js (module.js:442:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:311:12)
    at Function.Module.runMain (module.js:467:10)
    at startup (node.js:136:18)
    at node.js:963:3

Edit

Per one of the comments, I changed Option 2 to:

setTimeout(function () {
    Array.prototype.push.apply(arr1, arr2);
}, 0);

And I'm still getting:

/private/var/folders/j6/3fs5_k3n17z_0j2xrwj6sphw0000gn/T/CodeRunner/Untitled 9.js:16
    Array.prototype.push.apply(arr1, arr2);
                         ^

RangeError: Maximum call stack size exceeded
    at null._onTimeout (/private/var/folders/j6/3fs5_k3n17z_0j2xrwj6sphw0000gn/T/CodeRunner/Untitled 9.js:16:23)
    at Timer.listOnTimeout (timers.js:92:15)

"RangeError: Maximum call stack size exceeded" - What's your question? — Amit, Commented May 21, 2016 at 19:05
Stack Overflow. You went past the most things Javascript can do in a split second. Try doing setTimeout(function(){Array.prototype.push.apply(arr1, arr2);},0); and see if it helps — vtange, Commented May 21, 2016 at 19:10
@vtange I edited the question to reflect what you said. Why am I still getting this error? And not getting it on Option 1? — qarthandso, Commented May 21, 2016 at 19:19
@OlegV.Volkov if I'm getting a call stack error for the second option, why am I not getting it for the first? — qarthandso, Commented May 21, 2016 at 19:23

Oleg V. Volkov · Accepted Answer · 2016-05-25 14:15:37Z

4

The apply() method unrolls provided array to arguments list. ECMAScript specification itself have no limits on amount of arguments for function, but most JS engines have implementation-specifc limits because they use fixed or limited size structure for each function call on their internal stack for performance purposes. Though this limit is generally pretty high, it is certainly well below 10000000 arguments and that's why you get error "Maximum call stack size exceeded".

edited May 25, 2016 at 14:15

answered May 21, 2016 at 19:24

Oleg V. Volkov

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