if-else 的用法
var a = 33 if (a == 1){ console.log ('a等于1') } else if (a==2) { console.log ('a等于2') } else { console.log ('其他') }
![](https://upload-images.jianshu.io/upload_images/12904618-975e354f2eaf0abf.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/250)
switch-case 的用法
- switch使用常量时
var a=1 switch(a){ case 1: console.log('a等于1') break; case 2: console.log('a等于2') break; case 3: console.log('a等于3') break; default: console.log('其他') }
![](https://upload-images.jianshu.io/upload_images/12904618-3ee5f263a60b0235.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/284)
- switch使用表达式而非常量时
var a=33 switch(true){ case a>90: console.log('大于90') break; case a>80: console.log('大于80') break; case a>70: console.log('大于70') break; default: console.log('其他') }
![](https://upload-images.jianshu.io/upload_images/12904618-1a4494e0bbec67d5.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/279)
while 的用法
var i = 10; while(i>0) { console.log(i) i-- }
![](https://upload-images.jianshu.io/upload_images/12904618-92cf6f2c759cbda6.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/283)
do-while 的用法
var i = 4 do { console.log(i) i--; } while(i > 5);
![](https://upload-images.jianshu.io/upload_images/12904618-e5915c20f4a25d2e.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/220)
for 遍历数组的用法 (通过for遍历获得数组值的平方)
var arr=[3,4,5] for (i = 0 ; i < arr.length ; i++ ) { console.log(arr[i]*arr[i]) }
![](https://upload-images.jianshu.io/upload_images/12904618-295be4f0c9682f06.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/336)
for-in 遍历对象的用法
var object = {'a':1 , 'b':2 , 'c':3} for (var i in object) { console.log(i + ":" + object[i]) }
![](https://upload-images.jianshu.io/upload_images/12904618-508bca8d54df8a20.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/410)
break 和 continue 的用法
var i for ( i = 1; i<10 ;i++ ) { if(i%4 === 0){ break; } console.log(i) }
var i for ( i = 1; i<10 ;i++ ) { if(i%4 === 0){ continue; } console.log(i) }
![](https://upload-images.jianshu.io/upload_images/12904618-aa71226e97693cab.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/272)
![](https://upload-images.jianshu.io/upload_images/12904618-71fb0d81edef201c.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/282)