js day 01

1.变量的声明

var name='king';
console.log(name);

2.常亮的声明与赋值

const PI=3.55;
const PI=3.84;
console.log(PI);

3.js最基本的三种输出方式

console.log('hello king');
document.write('hello king')
alert('hello king');

4.变量的命名规范

var name='king';
var name1='king';
var name_1='king';
var $name='king';

5.变量的赋值

var name='king';
var name='queen';
console.log(name);
console.log(typeof name);

6.声明变量与未声明变量

//1.声明变量不赋值,返回undefined
    var hename
    console.log(hename);

//2.直接输出未声明的变量,会报错
    console.log(ahflk);