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how to measure function performance in javascript

Performance API

Performance Timeline API
Navigation Timing API
User Timing API
Resource Timing API.

https://developer.mozilla.org/en-US/docs/Web/API/Performance

performance.measure

performance.measure(name);
performance.measure(name, startMark);
performance.measure(name, startMark, endMark);
performance.measure(name, undefined, endMark);

performance.mark

performance.mark(name);

performance.now

const t1 = performance.now();

// do somethings

const t2 = performance.now();

High Resolution Time Level 2

W3C Recommendation 21 November 2019

https://www.w3.org/TR/hr-time/


const log = console.log;

const noForArrayAutoGenerator = (len = 100) => {
  return [...``.padStart(len, ` `)].map((item, i) => i + 1).map((item, i) => i % 2 === 0 ? item : item + ``);
}

const arr = noForArrayAutoGenerator(1000 * 100);

function test(arr = []) {
  const begin = performance.now();
  for (let i = 0; i < arr.length; i++) {
    // log(`item${i}`, arr[i]);
  }
  const end = performance.now();
  const result = end - begin;
  log(`result`, result)
}

test();

console.time & console.timeEnd

无返回值⚠️


const log = console.log;

console.time(`label`);

setTimeout(() => log(`zero`), 1000);
// 62

console.timeEnd(`label`);
// label: 16111.451171875 ms

https://developer.mozilla.org/en-US/docs/Web/API/Console/timeEnd

https://developer.mozilla.org/en-US/docs/Web/API/Console/time

console.log & new Date().getTime()


// new Date().getTime()

demos

"use strict";

/**
 *
 * @author xgqfrms
 * @license MIT
 * @copyright xgqfrms
 * @created 2020-07-20
 * @modified
 *
 * @description performance
 * @difficulty Easy Medium Hard
 * @complexity O(n)
 * @augments
 * @example
 * @link
 * @solutions
 *
 */

const log = console.log;

const noForArrayAutoGenerator = (len = 100) => {
  return [...``.padStart(len, ` `)].map((item, i) => i + 1).map((item, i) => i % 2 === 0 ? item : item + ``);
}

// const arr = noForArrayAutoGenerator(1);
// const arr = noForArrayAutoGenerator(100);
const arr = noForArrayAutoGenerator(10000);
// const arr = noForArrayAutoGenerator(10000 * 10);
// const arr = noForArrayAutoGenerator(10000 * 1000);

function test(arr = []) {
  // ReferenceError: performance is not defined
  const begin = performance.now();
  for (let i = 0; i < arr.length; i++) {
    // log(`item${i}`, arr[i]);
  }
  const end = performance.now();
  const result = end - begin;
  log(`result`, result)
}

test();