Run results for: JavaScript Array Copy

Run details:

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/121.0.0.0 Safari/537.36

Browser: Chrome 121

Operating system: Windows

Device Platform: Desktop

Date tested: 2 years ago

Test name	Executions per second
Array.concat	2389027.5 Ops/sec
Array.slice	2161545.8 Ops/sec
For loop	63111.4 Ops/sec
For loop with declared length	87453.3 Ops/sec
While loop	92879.5 Ops/sec
Spread operator	1869789.9 Ops/sec
Slice with begin argument	2367023.2 Ops/sec
Slice with begin and end argument	1864217.0 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