1：統(tǒng)計(jì)出數(shù)組中出現(xiàn)最多的值

(1)

var obj ={}
var arry = ['a','b','c','c','c','c','c','c','c','d','d','d','d','e','e','e','e','a','a','a','b']
arry.map(item=>{
    if(!obj[item]){
        obj[item] = 1
}else{
    obj[item] += 1
}
})
console.log(obj);
// {a: 4, b: 2, c: 7, d: 4, e: 4}

(2)

let arr = ['name','age','long','short','long','name','name'] 

let arrResult = arr.reduce((pre,cur) =>{
    console.log(pre,cur)
    if(cur in pre){
        pre[cur]++
    }else{
        pre[cur] = 1
    }
    return pre
},{})

console.log(arrResult)//結(jié)果：{name: 3, age: 1, long: 2, short: 1}

image.png

由于設(shè)置了迭代初始值，pre的第一個(gè)值是一個(gè)空對(duì)象，此時(shí)cur為name，然后進(jìn)行判斷，發(fā)現(xiàn)在pre中沒有name屬性，所以就將name對(duì)應(yīng)的屬性值賦為1；
后面沒有重復(fù)的是一樣的道理，如果碰到重復(fù)值，就會(huì)將該屬性值加1，這樣就能計(jì)算元素重復(fù)的次數(shù)了。

2：刪除數(shù)組中的假值

我們時(shí)常需要在處理數(shù)據(jù)的時(shí)候要去掉假值。在Javascript中，假值是false, 0， " "， null, NaN, undefined。

var plants = ['Saturn', 'Earth', null, undefined, false, "", NaN, 'Uranus', 'Mercury', 'Venus', 'Earth', 'Mars', 'Jupiter'];
var trueArr = plants.filter(Boolean);
console.log(trueArr); // ['Saturn', 'Earth','Uranus', 'Mercury','Venus', 'Earth','Mars', 'Jupiter']

3:數(shù)組如何快速轉(zhuǎn)變成對(duì)象存儲(chǔ)(擴(kuò)展運(yùn)算符)

let arr = ['key','jack','leaf','tree','cup','buddle','fish']
let obj = { ...arr }
console.log('obj',{0: "key", 1: "jack", 2: "leaf", 3: "tree", 4: "cup", 5: "buddle", 6: "fish"});