const a = [];
let target = [];

function noop(){};

for (let i = 0; i < 500000; ++i) a.push(Math.random());

console.time("push(...)");
target.push(...a);
console.timeEnd("push(...)");

target = [];

console.time("push.apply()");
target.push.apply(target, a);
console.timeEnd("push.apply()");

target = [];
console.time("splice()");
target.unshift(0, 0);
target.splice.apply(target, a);
console.timeEnd("splice()");

console.time("for () target.push(item)");
for (let i = 0; i < a.length; ++i) target.push(a[i]);
console.timeEnd("for () target.push(item)");

target = [];

console.time("noop(...)");
noop(...a);
console.timeEnd("noop(...)");

target = [];

console.time("noop.apply()");
noop.apply(window, a);
console.timeEnd("noop.apply()");

// RESULTS:
//
// push(...): 45.85ms
// push.apply(): 6.32ms
// splice(): 0.26ms
// for () target.push(item): 224.12ms
// noop(...): 40.5ms
// noop.apply(): 2.4ms