参考文献 https://juejin.cn/post/6925599792814882829
函数
call
语法：fn.call(obj,...args)
功能：执行fn，使this为obj，并将后面的n个参数传给fn
Function.prototype.myCall = function (obj, ...args) {
if (obj == undefined || obj == null) {
obj = globalThis
}
obj.fn = this
let res = obj.fn(...args)
delete obj.fn
return res
}
value = 2
let foo = {
value: 1,
}
let bar = function (name) {
console.log(name, this.value)
}
bar.myCall(foo, 'HearLing', 18) //HearLing 18 1
bar.myCall(null, 'HearLing', 18) //HearLing 18 2
apply
语法：fn.apply(obj,arr)
功能：执行fn，使this为obj，并arr数组中元素传给fn
Function.prototype.myAplly = function (obj, arr) {
if (obj == undefined || obj == null) {
obj = globalThis
}
obj.fn = this
let res = obj.fn(...arr)
delete obj.fn
return res
}
value = 2
let foo = {
value: 1,
}
let bar = function (name, age) {
console.log(name, age, this.value)
}
bar.myAplly(foo, ['HearLing', 18]) //HearLing 18 1
bar.myAplly(null, ['HearLing', 18]) //HearLing 18 2
bind
语法：fn.bind(obj,...args)
功能：返回一个新函数，给fn绑定this为obj，并制定参数为后面的n个参数
Function.prototype.myBind = function (obj, ...args) {
let that = this
let fn = function () {
if (this instanceof fn) {
return new that(...args)
} else {
return that.call(obj, ...args)
}
}
return fn
}
value = 2
let foo = {
value: 1,
}
let bar = function (name, age) {
console.log(name, age, this.value)
}
let fn = bar.myBind(foo, 'HearLing', 18)
//fn() //HearLing 18 1
let a = new fn() //HearLing 18 undefined
console.log(a.__proto__)//bar {}
区别call()/apply()/bind()
call(obj)/apply(obj)：:调用函数, 指定函数中的this为第一个参数的值bind(obj):返回一个新的函数, 新函数内部会调用原来的函数, 且this为bind()指定的第一参数的值
节流
理解：在函数多次频繁触发时，函数执行一次后，只有大于设定的执行周期后才会执行第二次
场景：页面滚动（scroll）、DOM 元素的拖拽（mousemove）、抢购点击（click）、播放事件算进度信息
功能：节流函数在设置的delay毫秒内最多执行一次（简单点说就是，我上个锁，不管你点了多少下，时间到了我才解锁）
function throttle(fn, delay) {
let flag = true
return (...args) => {
if (!flag) return
flag = false
setTimeout(() => {
fn.apply(this, args)
flag = true
}, delay)
}
}
防抖
理解：在函数频繁触发是，在规定之间以内，只让最后一次生效
场景：搜索框实时联想（keyup/input）、按钮点击太快，多次请求（登录、发短信）、窗口调整（resize）
功能：防抖函数在被调用后，延迟delay毫秒后调用，没到delay时间，你又点了，清空计时器重新计时，直到真的等了delay这么多秒。
function debounce(fn, delay) {
let timer = null
return (...args) => {
clearTimeout(timer)
timer = setTimeout(() => {
fn.apply(this, args)
}, delay)
}
}
curry
function mycurry(fn, beforeRoundArg = []) {
return function () {
let args = [...beforeRoundArg, ...arguments]
if (args.length < fn.length) {
return mycurry.call(this, fn, args)
} else {
return fn.apply(this, args)
}
}
}
function sum(a, b, c) {
return a + b + c
}
let sumFn = mycurry(sum)
console.log(sumFn(1)(2)(3))//6
数组
数组去重
function unique(arr) {
const res = []
const obj = {}
arr.foreach((item) => {
if (obj[item] === undefined) {
obj[item] = true
res.push(item)
}
})
return res
}
//其他方法
//Array.from(new Set(array))
//[...new Set(array)]
数组扁平化
// 递归展开
function flattern1(arr) {
let res = []
arr.foreach((item) => {
if (Array.isArray(item)) {
res.push(...flattern1(item))
} else {
res.push(item)
}
})
return res
}
对象
new
function newInstance (Fn, ...args) {
const obj = {}
obj.__proto__ = Fn.prototype
const result = Fn.call(obj, ...args)
// 如果Fn返回的是一个对象类型, 那返回的就不再是obj, 而是Fn返回的对象否则返回obj
return result instanceof Object ? result : obj
}
instanceof
function instance_of(left, right) {
let prototype = right.prototype
while (true) {
if (left === null) {
return false
} else if (left.__proto__ === prototype) {
return true
}
left = left.__proto__
}
}
let a = {}
console.log(instance_of(a, Object))//true
对象数组拷贝
浅拷贝
// 浅拷贝的方法
//Object.assign(target,...arr)
// [...arr]
// Array.prototype.slice()
// Array.prototype.concate()
function cloneShallow(origin) {
let target = {}
for (let key in origin) {
if (origin.hasOwnProperty(key)) {
target[key] = origin[key]
}
}
return target
}
let obj = {
name: 'lala',
skill: {
js: 1,
css: 2,
},
}
let newobj = cloneShallow(obj)
newobj.name = 'zhl'
newobj.skill.js = 99
console.log(obj)//{ name: 'lala', skill: { js: 99, css: 2 } }
console.log(newobj)//{ name: 'zhl', skill: { js: 99, css: 2 } }
深拷贝
// 深拷贝的方法
//JSON.parse(JSON.stringify(obj))
function deepClone(source, hashMap = new WeakMap()) {
let target = new source.constructor()
if (source == undefined || typeof source !== 'object') return source
if (source instanceof Date) return source(Date)
if (source instanceof RegExp) return source(RegExp)
hashMap.set(target, source)//解决循环引用
for (let key in source) {
if (source.hasOwnProperty(key)) {
target[key] = deepClone(source[key], hashMap)
}
}
return target
}
let obj = {//应该考虑更复杂的数据
name: 'lala',
skill: {
js: 1,
css: 2,
},
}
let newobj = deepClone(obj)
newobj.skill.js = 100
console.log(obj)//{ name: 'lala', skill: { js: 1, css: 2 } }
console.log(newobj)//{ name: 'lala', skill: { js: 99, css: 2 } }
