Javascript - Function access scope analysis 函数在页面上的可访问性浅析

本文链接：https://blog.youkuaiyun.com/yuxuac/article/details/48602181

我们知道，Javacript脚本可以定义在三个地方，Head标签中，Body标签中，Body标签之后。当定义一个函数的时候，你是否考虑过你在页面上什么位置可以访问这个函数，有没有规律可循：

As we know, people can define javascript block in 3 places, the Head block, the Body block and after the Body block. When you define a function within each block, have you ever considered at where you can call this function. Is there any order to follow:

<html>
	<head>
		<title>
			Pure Javascript test - Function Access Scope.
		</title>
		<script type="text/javascript">
			console.log("Javascrript code in head1.");
		</script>
		<script type="text/javascript">
			console.log("Javascrript code in head2.");
		</script>
	</head>
	<body>
		<script type="text/javascript">
			console.log("Javascript code in body before div.");
			Func1();
			function Func1(){
				console.log("I am Func1");
			}
			
		</script>
		<div>
			<h2>I am div between scripts in Body.</h2>
		</div>
		<script type="text/javascript">
			console.log("Javascript code in body after div.");
			
			Func1();
		</script>
	</body>
	<script type="text/javascript">
		console.log("Javascript code after body1.");
		Func1();
	</script>
	
	<script type="text/javascript">
		console.log("Javascript code after body2.");
		Func1();
	</script>
</html>

1. 定义在Head中第一个Script标签中的函数，可以被页面上任意Script标签内的脚本访问。

Functions defined in first script block in head, can be accessed by any script block in this page.

2. 定义在一个Script标签中的函数，可以被此Script标签中的任意脚本，和在此Script标签之下的定义的Script标签中的脚本访问。但是此函数不能被定义在此Script标签之上的Script标签中的脚本访问。

Functions defined in one script block, can be accessed within this block and blocks below, whereas they CAN NOT be accessed by blocks above current script block.