套路

//定义undefined

var a = undefined; //Before

var a = void 0;  //After

 

//获取时间戳 

(new Date()).getTime();  //Before

+(new Date());  //After 

 

//取整

parseInt(a,10); //Before

a>>0; //Before

~~a; //After

a|0; //After

 

//四舍五入

Math.round(a); //Before

a+.5|0; //After

  

//内置值

Infinity;

1/0;

 

//布尔值

true; //Before

!0; //After