全局作用域
全局作用域，就算不在一个script标签也能调用
<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><meta http-equiv="X-UA-Compatible" content="IE=edge"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head>
<body><script>var m = "aa"</script><script>console.log(m)</script>
</body>
</html> 
局部作用域
<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><meta http-equiv="X-UA-Compatible" content="IE=edge"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head>
<body><script>var m = "aa"// 定义全局函数testfunction test(){var b = "xiaoming"console.log("test",b,m)}// 在外边都访问不到bconsole.log(b)</script><script>// 可以调用全局变量mconsole.log(m)// 可以调用全局函数console.log(test)// 在外边都访问不到bconsole.log(b)test()</script>
</body>
</html> 