Run results for: JavaScript Array Copy

Run details:

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:102.0) Gecko/20100101 Firefox/102.0

Browser: Firefox 102

Operating system: Mac OS X 10.14

Device Platform: Desktop

Date tested: 2 years ago

Test name	Executions per second
Array.concat	2656859.0 Ops/sec
Array.slice	10126535.0 Ops/sec
For loop	685605.4 Ops/sec
For loop with declared length	621425.1 Ops/sec
While loop	232280.4 Ops/sec
Spread operator	1737836.6 Ops/sec
Slice with begin argument	10086431.0 Ops/sec
Slice with begin and end argument	10062549.0 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