JavaScript二

目录

流程控制

 if判断

while循环

do while

for循环

forEach

for in 

Map与set

iterator

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流程控制

 if判断

    <script>'use strict'var age = 5;if(age <= 3){alert("haha");}else if(age <= 5){alert("hi world");}else{alert("hello world");}</script>

while循环

    <script>'use strict'var age = 5;while(age < 100){age++;console.log(age);}</script>

do while

    <script>'use strict'var age = 5;do{age++;console.log(age);}while (age < 100);</script>

for循环

    <script>'use strict'for (let i = 0; i < 100; i++) {console.log(i);}</script>

forEach

    <script>'use strict'var arr = [1,2,3,4,5,6,6,7,8];arr.forEach(function (value) {console.log(value);});</script>

for in 

输出下标

    <script>'use strict'var arr = [12,23,3,44,5,6,26,57,8];for(var num in arr){console.log(arr[num]);}</script>

Map与set

 Map 

查找键对应的值

    <script>'use strict'var map = new Map([['tom',100],['jack',90],['hi',80]]);var sco = map.get('tom');console.log(sco);</script>

新增或者修改元素

    <script>'use strict'var map = new Map([['tom',100],['jack',90],['hi',80]]);map.set('admin',123456);var sco = map.get('admin');console.log(sco);</script>

删除元素

    <script>'use strict'var map = new Map([['tom',100],['jack',90],['hi',80]]);map.delete('tom');console.log(map);</script>

Set

 可以去重

    <script>'use strict'var set = new Set([1,1,1,2,34,4]);console.log(set);</script>

增加元素

    <script>'use strict'var set = new Set([1,1,1,2,34,4]);set.add(5);console.log(set);</script>

删除元素

    <script>'use strict'var set = new Set([1,1,1,2,34,4]);set.delete(5);console.log(set);</script>

查找是否包含元素

    <script>'use strict'var set = new Set([1,1,1,2,34,4]);console.log(set.has(1));</script>

iterator

推荐使用for of 进行遍历 

 遍历数组

    <script>'use strict'var arr = [11,22,3,4,5];for(var x of arr)console.log(x);</script>

遍历map

    <script>'use strict'var map = new Map([['tom',100],['jack',90],['hi',80]]);for(let x of map)console.log(x);</script>

遍历set

    <script>'use strict'let set = new Set([1,1,1,2,34,4]);for(let x of set)console.log(x);</script>