<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<script>
var a=5;
var b='5';
alert(a==b);//true 先转换类型再比较
alert(a===b);//false 不转换类型直接比较
</script>
</body>
</html>
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<script>
var a='12';
var b='5';
alert(a+b);//125 字符串连接 数字相加
alert(a-b);//7 数字相减
</script>
</body>
</html>
闭包：子函数可以使用父函数的局部变量