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Methods of declaring functions in JavaScript and return values of calling functions_Basic knowledge

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Release： 2016-05-16 16:41:27

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<html xmlns="http://www.w3.org/1999/xhtml"> 
<head> 
  <title></title> 
  <!--js中声明函数的方法--> 
  <script type="text/javascript"> 
    //因为javascript是弱类型的语言，所以参数不需要加类型。函数的也不需要像c#那样要求所以路径都需要有返回值（这个不像c#语言，而且c#的方法也不需要在方法名前面在 function关键字）  
 
    function add(i, j) { //现在只是声明了一个函数在这里，只有调用到它的时候它才会被执行。  
      return i + j; 
 
    } 
    alert(add(5, 6)); //输出11  
 
    //js中并非所有路径都有返回值，如果没有返回值他就认为返回值是undefined  
    function sum(x, y) { 
      if (x > y) { 
        alert(x + y); 
      }      
    } 
    var z = sum(2, 6); //因为2并不大于6所以sum函数就没有返回值。如果没有返回值他就认为返回值是undefined。  
    alert(z); //所以它就输出了undefined  
         
  </script> 
</head> 
<body> 
 
</body> 
</html>

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