import { createBenchmark } from "./benchmark";
class MyArray extends Array {}
const SIZE = 100;
const obj: Record<string, number> = {};
/**
* {
* _0: 0,
* _1: 1,
* _2: 2,
* ...
* }
*/
const array = [];
/**
* [
* '_0', 0,
* '_1', 1,
* '_2', 2,
* ...
* }
*/
for (let i = 0; i < SIZE; i++) {
obj["_" + i] = i;
array.push("_" + i, i);
}
(function doBenchmarks(benchmark) {
(function benchmark1(obj, timer) {
let sum = 0;
while (timer()) {
for (const key in obj) {
sum += obj[key];
}
}
})(obj, benchmark("property"));
(function benchmark1(obj, timer) {
let sum = 0;
while (timer()) {
const copy = { ...obj };
for (const key in copy) {
sum += copy[key];
}
}
})(obj, benchmark("property with copy"));
(function benchmark2(array, timer) {
let sum = 0;
while (timer()) {
for (let i = 0; i < array.length; i += 2) {
sum += array[i] as number;
}
}
})(array, benchmark("array"));
(function benchmark2(array, timer) {
let sum = 0;
while (timer()) {
const copy = array.slice();
for (let i = 0; i < copy.length; i += 2) {
sum += copy[i] as number;
}
}
})(array, benchmark("array with copy"));
benchmark.report();
})(createBenchmark("iteration"));
From the result we can see that, using array.slice()to copy a array is quite light weight operation, it doesn't affect performance that much.
But using {...obj}is expensive, it affect performance by a lot.
It is due to the hidden class of the object, everytime you push a new prop into object it will create a new hidden class.