Run results for: JS insert at index spread vs Splice

Run details:

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.114 Safari/537.36

Browser: Chrome 91

Operating system: Mac OS X 10.15.7

Device Platform: Desktop

Date tested: 3 years ago

Test name	Executions per second
Array update with spread operator	2232753.2 Ops/sec
Array update with slice and assign	2067800.0 Ops/sec

Script Preparation code:

const ITERATIONS = 500000;
var index = ITERATIONS/2;
var n = Math.random();

var list = [];
for (let i = 0; i < length; i += 1) {
  list.push(Math.random());
}

Tests:

Array update with spread operator
const clone = [ ...list.slice(0, index), n, ...list.slice(index + 1), ];
Array update with slice and assign
const clone = list.slice(); clone[index] = n;

Run results for: JS insert at index spread vs Splice

Array update with spread operator

Array update with slice and assign