Run results for: JavaScript Array Copy

Run details:

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:132.0) Gecko/20100101 Firefox/132.0

Browser: Firefox 132

Operating system: Windows

Device Platform: Desktop

Date tested: one year ago

Test name	Executions per second
Array.concat	12661375.0 Ops/sec
Array.slice	15927374.0 Ops/sec
For loop	637280.8 Ops/sec
For loop with declared length	252474.2 Ops/sec
While loop	44998.5 Ops/sec
Spread operator	3167061.5 Ops/sec
Slice with begin argument	14433006.0 Ops/sec
Slice with begin and end argument	15062909.0 Ops/sec

Script Preparation code:

var arrayToCopy = [ "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello" ];
var shallowCopy = [];

Tests:

Array.concat
shallowCopy = arrayToCopy.concat();
Array.slice
shallowCopy = arrayToCopy.slice();
For loop
for (let i = 0; i < arrayToCopy.length; ++i) { shallowCopy.push(arrayToCopy[i]); }
For loop with declared length
var arrayLength = arrayToCopy.length; for (let i = 0; i < arrayLength; ++i) { shallowCopy.push(arrayToCopy[i]); }
While loop
let i = arrayToCopy.length - 1; while (i--) { shallowCopy.push(arrayToCopy[i]); }
Spread operator
shallowCopy = [...arrayToCopy];
Slice with begin argument
shallowCopy = arrayToCopy.slice(0);
Slice with begin and end argument
shallowCopy = arrayToCopy.slice(0, arrayToCopy.length);

Run results for: JavaScript Array Copy

Testing the results for the fastest approach of shallow copying an array in JavaScript (concat, slice, for loop, and while loop).

Array.concat

Array.slice

For loop

For loop with declared length

While loop

Spread operator

Slice with begin argument

Slice with begin and end argument