js day02

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);