初识Javascript
<head>
<meta charset="utf-8"/>
<title></title>
<script>
js代码内部引入方法1
alert('iiii')
alert('1234')
</script>
</head>
<body>
js代码内部引入方法2
<script type='text/javascript'>
alert('李青是猪🐖');
</script>
外部引入
<scrtpt src="script/js/名称.js" type="text/javascript" charset="utf-8"></script>
<noscript>
您的浏览器不支持javascript,请更换查看
</noscript>
行内引入
<a href="javascript:confirm('您确认要学习Javascript吗?');">报名</a>
<p onclick="javascript:alert('hello word');">clickMe</p>
以上是引入方式
<script type="text/javascript">
var a;
var b;
var c,d;
var test = 'this is a test';
var test1 = '12';
var test2 = 1.2;
var test3 = true;
var test4 = false;
var a = b = c = d = e = 1;
a=33;
var username = 'king';
var userName = 'QUEEN';
var age = 12;
var test5 = 'hello';
var _test = 'hello';
document.write('aaa');
document.write('<br />');
document.write('bbb');
alert('<h1>rrrrrr</h1>')
document.write('ccc');
document.write('ddd');
document.write('<br />');
document.write('hello \
world');\
变量名称最好含义明确,以字母或者下划线开头,跟上数字字母下划线
var age=12;
var test5= 'hello';
var 12a='bb';
alert(12a);
var _test='hello';
alert(_test);
驼峰标记法和下划线
var firstName = 'king';//小驼峰
var FirstName = 'queen';//大驼峰
var first_name = 'ymt';//下划线法
console.log('向控制台中书写内容');
</script>
a = 0;
a = 0.0;
a = 0/0;
//alert(a); //not a number
//NaN
a = NaN;
//alert(typeof Number(NaN));
var a ="";//空字符集->false
//a=0;
//a= null;
var b=0;
console.log( a == b);
//null != 0
//null != ""
//null == undefined
//0 != undefined
//" " != undefined
//" " == 0
