Run results for: Array.prototype.concat vs Array.prototype.splice

Run details:

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/101.0.4951.54 Safari/537.36

Browser: Chrome 101

Operating system: Windows

Device Platform: Desktop

Date tested: 2 years ago

Test name	Executions per second
immutable with concat	780.5 Ops/sec
direct mutation with splice	2149.5 Ops/sec

Script Preparation code:

var a = [];
var b = [];
for (let i = 0; i < 200000; i++) {
  let s = i.toString();
  a.push(s);
  b.push(s);
}

Tests:

immutable with concat
a.slice(0, 100000).concat(b, a.slice(100000))
direct mutation with splice
let pos_a = 100000; let pos_b = 0; for (let i = 0; i < 4; i++) { a.splice(pos_a, 0, ...(b.slice(pos_b, pos_b + 50000))); pos_a += 50000; pos_b += 50000; }