Run results for: Array.prototype.concat vs splice for joining many arrays

Run details:

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/86.0.4240.75 Safari/537.36

Browser: Chrome 86

Operating system: Windows

Device Platform: Desktop

Date tested: 4 years ago

Test name	Executions per second
immutable with concat	0.4 Ops/sec
direct mutation with splice + spread	301.0 Ops/sec

Tests:

immutable with concat
var a = [ "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 other = []; for(const x of Array(10000)) { other = other.concat(a) }
direct mutation with splice + spread
var a = [ "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 other = []; for(const x of Array(10000)) { other.splice(other.length, 0, ...a); }