强制转换

1-1.字符串转number

函数 number();

var str = "12";
console.log(Number(str)) //12
var s = "";
var p = " ";
console.log(Number(s))
console.log(Number(p))

srring转number

string-->number
parseInt();  "12px";
parseFloat(); "12.434px";
console.log(Number("12px")) //NaN

1-2 boolean转number

Number(true) //1
Number(false) //0

1-3 number转boolean

tips: 0转换为false,其他都为true

1-4 string转boolean

tips:””为false,其他都为true

1-5 number转string

String();
toString();
+””;