作用域解析及作用域链

来源：互联网发布：婚礼现场互动软件编辑：程序博客网时间：2024/05/16 12:20

预解析遇到重名，只留一个。如果与函数重名，就只留下函数。

 console.log(a);// function a(){console.log(4)}    var a = 1;    console.log(a); // 1    function a(){        console.log(2);    }    console.log(a);// 1    var a = 3;    console.log(a); //3    function a() {        console.log(4);    }    console.log(a());//报错

自上而下，由内而外

 <script type="text/javascript">      alert(a);//报错  </script>   <script type="text/javascript">      var a = 1;  </script>-------------------------------------------------- <script type="text/javascript">      var a = 1;   </script>   <script type="text/javascript">     alert(a);//1  </script>

var a = 1;function test() {    alert(a);    var a = 2;}alert(a);//1test();// undefined

var a = 1;function test() {    alert(a);    a = 2;}test();// 1alert(a);// 2

var a = 1;function test() {    alert(a);    a = 2;}alert(a);// 1test();// 1

var a = 1;function test(a) {    alert(a);    a = 2;}test();// undefinedalert(a);// 1

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