Run results for: Big Array prepend

Run details:

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/83.0.4103.116 Safari/537.36

Browser: Chrome 83

Operating system: Mac OS X 10.15.4

Device Platform: Desktop

Date tested: 3 years ago

Test name	Executions per second
Spread Operator	8107.9 Ops/sec
Unshift	9149.0 Ops/sec
Unshift without mutation	8510.9 Ops/sec
Prepend function	2551.1 Ops/sec

Script Preparation code:

var a;
var prependArray = function(value, oldArray) {
    var i, len = oldArray.length + 1,
        newArray = new Array(len);
    newArray[0] = value;
    for (i = 0; i < len; ++i) {
        newArray.push(oldArray[i]);
    }
    return newArray;
}

Tests:

Spread Operator
a = new Array(10000).fill().map((_, i) => i) a = [0, ...a];
Unshift
a = new Array(10000).fill().map((_, i) => i) a.unshift(0);
Unshift without mutation
a = new Array(10000).fill().map((_, i) => i) a.slice(0).unshift(0);
Prepend function
a = new Array(10000).fill().map((_, i) => i) prependArray(0, a);

Run results for: Big Array prepend

Spread Operator

Unshift

Unshift without mutation

Prepend function