3、强制转换

1、强制数据类型转换

1-1 string,boolean—>number

1-1-1纯数字string—>number

特点:只能识别纯数字的字符串
Number(value)
var a = "10";
var str = "hello"
console.log(Number(a))  //10
console.log(Number(str)) //NaN  不是一个数字
console.log(Number("3.0")) //3
console.log(Number(undefined)) // NaN

1-1-2 boolean —>number

var t = true
var f = false
console.log(Number(t));    //1
console.log(Number(f));    //0

1-1-3、含有字符的string—>number

parseInt()
parseFloat()
  var str = "12px"
  var s = "12.34px"
  console.log(parseInt(str));
  console.log(parseFloat(s));

1-2 number,string—>boolean
1-2-1 number—boolean

Boolean()
0转换为false，其他都为true

1-2-2 string—>boolean

""为false，其他都为true

1-3 Any-String

String()
toString()
+""