js-------类型转换

1、转换为number

　　(1) parseInt()  转换为整数

console.log(parseInt("10"));   //10
console.log(parseInt("10afre"));   //10
console.log(parseInt("g10"));   //NaN
console.log(parseInt("1fg0p"));   //1
console.log(parseInt("10.98"));   //10
console.log(parseInt("10.98fd"));   //10

　　(2)parseFloat()  转换为小数

console.log(parseFloat("10"));   //10
console.log(parseFloat("10afre"));   //10
console.log(parseFloat("g10"));   //NaN
console.log(parseFloat("1fg0p"));   //1
console.log(parseFloat("10.98"));   //10.98
console.log(parseFloat("10.98fd"));   //10.98

　　(3)Number()   转换为数字

console.log(Number("10"));   //10
console.log(Number("10afre"));   //NaN
console.log(Number("g10"));   //NaN
console.log(Number("1fg0p"));   //NaN
console.log(Number("10.98"));   //10.98
console.log(Number("10.98fd"));   //NaN

2、转换为string类型

　　(1)  .toString()

var num=1;
console.log(num.toString)

　　(2)  String()

var num1=1;
console.log(String(num1));

var num2;
console.log(String(num2));  //这种特殊情况用String

var num3=null;
console.log(String(num3));   //这种特殊情况用String

3、转换为Boolean类型

　　(1) Boolean()

console.log(Boolean(1));   //true
console.log(Boolean(0));   //false
console.log(Boolean(11));   //true
console.log(Boolean(-11));   //true
console.log(Boolean("哈哈"));   //true
console.log(Boolean(""));   //false
console.log(Boolean(null));   //false
console.log(Boolean(undefined));   //false