1. JavaScript对大小写敏感。
2. JavaScript是脚本语言。浏览器会在读取代码时，逐行地执行脚本代码。而对于传统编程来说，会在执行前对所有代码进行编译。
3. 变量什么用var, 是弱类型。
JavaScript数据类型：数字、字符串、布尔、数组、对象、null、undefined
JavaScript变量均为对象。当你声明一个变量时，就创建了一个新的对象。
<!DOCTYPE html>
<html>
<head>
<title></title>
<meta charset="utf-8" />
</head>
<body>
<script>
document.write("Hello
World" + "</br>");
var x;// undefined
var n = null;//null
var y = 6;//数字
var f = 3.1415;//浮点数
var s = "Hello World";//字符串
var carname = '大众';//也可以单引号
var answer1 = "He is called 'yoyo'";
var answer2 = 'He is called"yoyo"';
var b = true;//bool型
//JavaScript变量均为对象，当您声明一个变量时，就创建了一个新的对象
var z1 = new Number;
var z2 = new String;
var z3 = new Boolean;
var z4 = new Array;
var z5 = new Object;
//数组
var cars1 = new Array();
cars1[0] = "Audi";
cars1[1] = "BMW";
cars1[2] = "Volvo";
var cars2 = new Array("Audi", "BMW", "Volvo");
var cars3 = ["Audi", "BMW", "Volvo"];
//对象：对象由花括号分隔。在括号内部，对象的属性以名称和值对的形式来定义
var person = {
firstname: "yoyo",
lastname: "xiao",
id: 506
};
document.write(x + "</br>");
document.write(n+ "</br>");
document.write(y + "</br>");
document.write(f + "</br>");
document.write(s + "</br>");
document.write(carname + "</br>");
document.write(answer1 + "</br>");
document.write(answer2 + "</br>");
document.write(b + "</br>");
document.write(z1 + "</br>");
document.write(z2 + "</br>");
document.write(z3 + "</br>");
document.write(z4 + "</br>");
document.write(z5 + "</br>");
for (i = 0; i < cars3.length;i++)
{
document.write(cars3[i] + "</br>");
}
document.write(person.firstname + "</br>");
document.write(person["lastname"] + "</br>");
</script>
</body>
</html>