javascript 笔记之做用域

<script type="text/javascript">
/**
 * 做用域:在嵌套的函数中变量的寻址是由里向外的，当寻址到变量的值就不会继续在往外找。找到window对象时无此属性会报undefined错误
 */	
  function out(){
  	var d=5;
	function into(){
		var e=5;
		var d=2
		alert(d+e);
	}
	into();
  }
  out(); // 输出为7
</script>

+-----------------------------------------------------------------------------------------------------------------------------
<script type="text/javascript">
/**
 * var 关键字：只是变量的定义而已，并不表明做用域,未加关键字var的变量只至关于赋值操做.
 */	
 alert(window.e); // undefined
 alert(window.d); // undefined
 function  t(){
 	e=5;
	var d=6
 } 
 t();
 alert(window.e); //  5
 alert(window.d); //  undefined
</script>

+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

<script type="text/javascript">
/**
 * 代码的运行方式是自上而下从左至右，从函数里到外
 */	
 var str1='global';
 function t(){
 	alert(str1);
	alert(str2);
	str2='aa';
 }
 t();
 output:
 global;
 undefined;
</script>