1.實現(xiàn)lodash的_.get方法
function _getValue(target, valuePath, defalutVal) {
let valueType = Object.prototype.toString.call(target)
console.log(valueType)
// if (valueType == "[object Array]") {
let paths = valuePath.replace(/\[(\d+)\]/, `.$1`).split('.')
let result = target
for(const path of paths){
result = Object(result)[path]
if(result == undefined){
return defalutVal
}
}
return result
}
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測試:
let obj = {
a:{
b:[
{
c:2
}
]
}
}
console.log(_getValue(obj, 'a.b[0].c')) //2
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2.寫一個函數(shù)判斷兩個變量是否相等
function isEqual(res1, res2) {
let a = getTypeOf(res1)
let b = getTypeOf(res2)
if(a !== b){
return false
}else if(a === 'base'){
console.log('base',res1,res2)
return res1 === res2
} else if(a === 'array'){
if(res1.length !== res2.length){
console.log('array',res1,res2)
return false
}else{
//遍歷數(shù)組的值比較
for(let i =0;i<res1.length;i++){
if(!isEqual(res1[i],res2[i])){
console.log('array',res1[i],res2[i])
return false
}
}
return true
}
return true
}else if(a === 'object'){
let ak = Object.keys(a)
let bk = Object.keys(b)
if(ak.length !== bk.length){
return false
}else{
for(let o in res1){
console.log(res1[o])
if(!isEqual(res1[o],res2[o])){
console.log('object',res1[o],res2[o])
return false
}
}
return true
}
}else if(a === 'null' || a === 'undefined'){
console.log('null')
return true
}else if(a === 'function'){
console.log('function')
return a === b
}
}
function getTypeOf(res) {
let type = Object.prototype.toString.call(res)
switch (type) {
case "[object Array]":
return 'array'
case "[object Object]":
return 'object'
case "[object Null]":
return 'null'
case "[object Undefined]":
return 'undefined'
case "[object Number]"||"[object String]"||"[object Boolean]":
return 'base'
case "[object Function]":
return 'function'
default:
return 'typeError'
}
}
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測試:
let a = {
a:20,
b:{
c:30,
d:[1,2,3]
}
}
let b = {
a:20,
b:{
c:30,
d:[1,2,3]
}
}
console.log(isEqual(a,b)) //true
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3.數(shù)組扁平化的方法
function _flat(arr){
let result = []
for(let i = 0;i<arr.length;i++){
if(Array.isArray(arr[i])){
result = result.concat(_flat(arr[i]))
}else{
result.push(arr[i])
}
}
return result;
}
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let arr = [1,2,[3,4,[5,6]]]
_flat(arr) //[1,2,3,4,5,6]
//es6
function _flat2(arr){
while(arr.some(item=>Array.isArray(item))){
arr = [].concat(...arr)
}
return arr
}
let arr = [1,2,[3,4,[5,6]]]
_flat2(arr) //[1,2,3,4,5,6]
4.深克隆
簡單深克隆，不考慮內置對象和函數(shù)
function deepClone(obj){
if(typeof obj !== 'object') return
let newObj = obj instanceof Array?[]:{}
for(let key in obj){
if(obj.hasOwnProperty(key)){
newObj[key] = typeof obj[key] === 'object'?deepClone(obj[key]):obj[key]
}
}
return newObj
}
復雜版深度克隆 考慮內置對象 比如date regexp 函數(shù) 以及對象的循環(huán)引用的問題
const isObject = (target) => typeof target === "object"&& target !== null;
function deepClone2(target, map = new WeakMap()) {
console.log(target)
if (map.get(target)) {
return target;
}
// 獲取當前值的構造函數(shù)：獲取它的類型
let constructor = target.constructor;
// 檢測當前對象target是否與正則、日期格式對象匹配
if (/^(RegExp|Date)$/i.test(constructor.name)) {
// 創(chuàng)建一個新的特殊對象(正則類/日期類)的實例
return new constructor(target);
}
if (isObject(target)) {
map.set(target, true); // 為循環(huán)引用的對象做標記
const cloneTarget = Array.isArray(target) ? [] : {};
for (let prop in target) {
if (target.hasOwnProperty(prop)) {
cloneTarget[prop] = deepClone(target[prop], map);
}
}
return cloneTarget;
} else {
return target;
}
}
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5.數(shù)組去重
filter去重
function _unique(arr){
return arr.filter((item,index,array)=>{
return array.indexOf(item) === index
})
}
es6 Set
function _unique2(arr){
return [...new Set(arr)]
}
includes
function _unique3(arr){
let newArr = []
arr.forEach(item => {
if(!newArr.includes(item)){
newArr.push(item)
}
});
return newArr
}
雙層for循環(huán)
function _unique4(arr){
for(let i =0;i<arr.length;i++){
for(let j =i+1;j<arr.length;j++){
if(arr[i] === arr[j]){
arr.splice(j,1)
j--
}
}
}
return arr
}
indexof
function _unique5(arr){
let newArr = []
for(let i = 0;i<arr.length;i++){
if(newArr.indexOf(arr[i] === -1){
newArr.push(arr[i])
})
}
return newArr
}
6.判斷數(shù)據(jù)的類型
function _typeOf(obj){
let res = Object.prototype.toString.call(obj).split(' ')[1]
let mold = res.substring(0,res.length-1).toLowerCase()
return mold
}
_typeOf（5） //number
_typeOf（'5'） //string
7.解析url參數(shù)為對象
function getParamsObj(params){
let paramsStr = params.replace(/^.+\?(.+)/,"$1")
let paramsArr = paramsStr.split('&')
let paramsObj = {}
for(let [key,value] of paramsArr.entries()){
if(/=/.test(value)){
let valArr = value.split('=')
val = decodeURIComponent(valArr[1]) //解碼
val = /^\d+$/.test(val)?parseFloat(val):val //判斷是不是數(shù)字
if(paramsObj.hasOwnProperty(valArr[0])){
paramsObj[valArr[0]] = [].concat(paramsObj[valArr[0]],val)
}else{
paramsObj[valArr[0]] = val
}
}
}
return paramsObj
}
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8.函數(shù)柯里化
//從一次傳入多個參數(shù) 編程多次調用每次傳入一個參數(shù)
function add(a, b, c, d, e) {
return a + b + c + d + e
}
function curry(fn) {
let dFn = (...args)=>{
if(args.length == fn.length) return fn(...args)
return (...arg)=>{
return dFn(...args,...arg)
}
}
return dFn
}
let addCurry = curry(add)
addCurry(1,2,3)(2)(3)
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9.圖片懶加載
//添加了兩個功能
// 圖片加載完成后 移除事件監(jiān)聽
// 加載完的圖片從imgList中移除
let imgList = [...document.querySelectorAll('img')]
let length = imgList.length
const imgLazyLoad = function () {
let count = 0
let deleteIndexList = []
imgList.forEach((img, index) => {
let rect = img.getBoundingClientRect()
//獲取元素到視圖的距離 top元素上邊到視圖上邊的距離 left元素左邊到視圖左邊的距離 right... bottom...
if (rect.top < window.innerHeight) {
// img.src = img.dataset.src
img.src = img.getAttribute('data-src')
deleteIndexList.push(index)
count++
if (count === length) {
document.removeEventListener('scroll', imgLazyLoad)
}
}
})
imgList = imgList.filter((img, index) => !deleteIndexList.includes(index))
}
imgLazyLoad()
document.addEventListener('scroll', imgLazyLoad)
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圖片懶加載:https://juejin.cn/post/6844903856489365518#heading-19
10節(jié)流防抖
函數(shù)防抖 觸發(fā)高頻事件 事件在n后執(zhí)行，如果n秒鐘重復執(zhí)行了 則時間重置
//簡易版
function debounce(func,wait){
let timer;
return function(){
let context = this;
let args = arguments;
console.log(timer)
clearTimeout(timer)
timer = setTimeout(function(){
func.apply(context,args)
},wait)
}
}
let btn = document.querySelector('button');
function aa(){
console.log(111)
}
btn.onclick = debounce(aa,2000)
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// 復雜版
// 1.取消防抖
// 2.立即執(zhí)行功能（點擊之后立即執(zhí)行函數(shù) 但是 wait時間之后在點擊才能在立即執(zhí)行）
// 3.函數(shù)可能有返回值
function debounce(func,wait,immediate){
let timer,result;
const debounce = function () {
const context = this
const args = arguments
if(timer) clearTimeout(timer)
if(immediate){
console.log(timer)
var callNow = !timer
timer = setTimeout(function () {
timer =null
},wait)
if(callNow) result = func.apply(context,args)
}else{
timer = setTimeout(function (params) {
result = func.apply(context,args)
},wait)
}
return result
}
debounce.cance = function () {
clearTimeout(timer)
timer=null
}
return debounce
}
let btn = document.querySelector('button');
function aa(){
console.log(111)
}
btn.onclick = debounce(aa,2000,true)```
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函數(shù)節(jié)流 觸發(fā)高頻事件 且n秒只執(zhí)行一次
//使用時間戳
function throttle(func,wait) {
var context,args;
var previous = 0
return function () {
context = this;
args = arguments;
let nowDate = +new Date()
if(nowDate-previous>wait){
func.apply(context,arguments)
previous = nowDate
}
}
}
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//定時器
function throttle(func,wait) {
var context,args;
var timer;
return function(){
context = this;
args = arguments;
if(!timer){
timer = setTimeout(function () {
timer = null;
func.apply(context,args)
},wait)
}
}
}
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//組合版 options.leading 為true 立即執(zhí)行一次 options.trailing為true 結束之后執(zhí)行一次 默認為true
function throttle(func, wait ,options = {}) {
var context, args, timer,result;
var previous = 0;
var later = function () {
previous = options.leading === false ? 0 : new Date().getTime();
timer = null;
func.apply(context, args)
if (!timer) context = args = null;
}
var throttle = function () {
var now = new Date().getTime()
if (!previous && options.leading === false) previous = now;
context = this;
args = arguments;
//下次觸發(fā) func 剩余的時間
var remaining = wait - (now - previous);
if (remaining <= 0 || remaining > wait) {
// if (timer) {
// clearTimeout(timer);
// timer = null;
// }
previous = now;
func.apply(context, args);
if (!timer) context = args = null;
} else if (!timer&& options.trailing !== false) {
timer = setTimeout(later, remaining);
}
}
throttled.cancel = function() {
clearTimeout(timer);
previous = 0;
timer = null;
}
return throttle
}
function aa(e) {
console.log(111)
console.log(e)
}
let btn = document.querySelector('button');
btn.onclick = throttle(aa, 2000,{
leading:false,
trailing:true
})
轉自：csdn論壇 作者：Selfimpr歐
