JS基础_函数作用域练习

 <!DOCTYPE html>

 <html>

     <head>

         <meta charset="UTF-8">

         <title></title>

         <script type="text/javascript">

             var a = 123;

             function fun(){

                 alert(a);//undefined

                 var a = 456;

                 alert(a);//456

             }

             fun();

             alert(a);//123

             //---------------------------------------------------

             var b = 123;

             function fun(){

                 alert("b = "+b);//123

                 b = 456;

             }

             fun();

             alert("b = "+b);//456,全局的b变成了456

             //---------------------------------------------------

             var c = 123;

             function fun(c){

                 alert("c = "+c);//undefined

                 c = 456;//对外面的c没影响

             }

             fun();

             alert("c = "+c);//123

             //---------------------------------------------------

             var d = 123;

             function fun(d){

                 alert("d1 = "+d);//789

                 d = 456;

             }

             fun(789);

             alert("d = "+d);//123

         </script>

     </head>

     <body>

     </body>

 </html>
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JS基础_函数作用域练习

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