js 2

1.数据类型的转换

number

var num1=10;

var num2=16;

string

var str1='king';

boolean

var boo=true;

var oo2=false;

undefined

var undef;

1)number + number = number

var num3=num1+num2;

console.log(num3);//26

console.log(typeof num3);

2)number + string = string

var str=num1+str1;

console.log(str);//10hello

console.log(typeof str);

3)number + boolean = number

var boo=num1+boo1;

console.log(boo);//11

console.log(typeof boo);

4)number + undefined = number

var und=num1+undef;

console.log(und);//NAN

console.log(typeof und);

5)string + boolean = string

var stb=str1+boo1;

console.log(stb); //kingtrue

console.log(typeof stb);

6)string + undefined = string

var sfind=str1+undef;

console.log(sfind);/kingundefined

console.log(typeof sfind);

2.数据类型转换减法操作

var num1 = 10;

var str1 = "11";

var str2 = "Hello";

var str3 = "35";

var str4 = "waht";

console.log(num1+str1);//1011

console.log(num1-str1);// -1

console.log(str1+str3);//1135

console.log(str3-str1);//24

console.log(str2-str4);//NaN

3.强制转换

整数

var  num=6;

var str=num.toString();

console.log(str);//6

console.log(typeof str);//string

小数

var  num=6.6;

var str1=parseInt(num);

console.log(str1);//6

console.log(typeof str1);//number

小数点后几位

var  num=.0666;

var str2=parseFloat(num);

console.log(str2);//0.666

console.log(typeof str2);//number

字母

var str="abc";

var str3=isNaN(str);

console.log(str3);//true

console.log(typeof str3);//boolean

4.运算符-逻辑运算符

var num = parseInt(prompt("请输入一个数字"));

//判断 num 是否在 0~10之间

var result=(num>=0&&num<=10);

console.log(num+"在0~10之间吗?"+result);