javascript - 性能:typeof vs instanceof

Question

我想知道 typeof 中的哪一个和 instanceof性能更高，所以我把以下小东西放在一起:

let TIMES = 1000 * 1000 * 100

console.time("(() => { }) instanceof Function")
for (let i = 0; i < TIMES; i++)
  (() => { }) instanceof Function
console.timeEnd("(() => { }) instanceof Function")

console.time("(async () => { }) instanceof Function")
for (let i = 0; i < TIMES; i++)
  (async () => { }) instanceof Function
console.timeEnd("(async () => { }) instanceof Function")

console.time("(function () { }) instanceof Function")
for (let i = 0; i < TIMES; i++)
  (function () { }) instanceof Function
console.timeEnd("(function () { }) instanceof Function")

console.time("(async function () { }) instanceof Function")
for (let i = 0; i < TIMES; i++)
  (async function () { }) instanceof Function
console.timeEnd("(async function () { }) instanceof Function")

console.time("typeof (() => { }) === 'function'")
for (let i = 0; i < TIMES; i++)
  typeof (() => { }) === 'function'
console.timeEnd("typeof (() => { }) === 'function'")

console.time("typeof (async () => { }) === 'function'")
for (let i = 0; i < TIMES; i++)
  typeof (async () => { }) === 'function'
console.timeEnd("typeof (async () => { }) === 'function'")

console.time("typeof (function () { }) === 'function'")
for (let i = 0; i < TIMES; i++)
  typeof (function () { }) === 'function'
console.timeEnd("typeof (function () { }) === 'function'")

console.time("typeof (async function () { }) === 'function'")
for (let i = 0; i < TIMES; i++)
  typeof (async function () { }) === 'function'
console.timeEnd("typeof (async function () { }) === 'function'")

并从 Chrome 66 的控制台获得了这些超酷的结果:

(() => { }) instanceof Function: 1789.844970703125ms
(async () => { }) instanceof Function: 2229.64208984375ms
(function () { }) instanceof Function: 1954.09716796875ms
(async function () { }) instanceof Function: 2279.995849609375ms
typeof (() => { }) === 'function': 412.8701171875ms
typeof (async () => { }) === 'function': 413.337890625ms
typeof (function () { }) === 'function': 413.387939453125ms
typeof (async function () { }) === 'function': 412.910888671875ms

Firefox 59 花了很长时间才能运行该 XD

我没有足够的耐心等待它并且使TIMES减少了十倍:

let TIMES = 1000 * 1000 * 10

有了这个，我从 Firefox 59 的控制台中得到了以下信息:

(() => { }) instanceof Function: 5490ms
(async () => { }) instanceof Function: 6884ms
(function () { }) instanceof Function: 5408ms
(async function () { }) instanceof Function: 6938ms
typeof (() => { }) === 'function': 1916ms
typeof (async () => { }) === 'function': 1998ms
typeof (function () { }) === 'function': 1976ms
typeof (async function () { }) === 'function': 1972ms

两个结果集都显示 typeof比 instanceof 快得多，其他几个人也在 Which is best to use: typeof or instanceof? 中提到的事实.

我的问题是“你”？

Answer 1

正如您还预测并展示了来自 SO 的其他链接，typeof会更快(jsperf : https://jsperf.com/instanceof-vs-typeof/5)，这是有道理的，因为 typeof当您控制 instanceof 的右侧时，将返回其中一种内置类型( 对象、未定义和原语 )操作数。这意味着 instanceof运算符(operator)应检查 原型(prototype)链 并查看右侧是否已用作 构造函数 沿着某处。这自然是更多的工作。