如何覆盖JavaScript函数

在本文中，我们提供了一个HTML文档，并且任务是使用JavaScript覆盖函数，无论是预定义函数还是用户定义函数。

方法： 当我们运行脚本时，将调用Fun()函数。点击按钮后，将调用 GFG_Fun() 函数，该函数包含另一个将运行的函数。

示例1： 在这个示例中，用户编写的函数被覆盖。

<body style="text-align:center;"> 
  
    <h1 style="color:green;" id="h1"> 
        GeeksForGeeks 
    </h1> 
  
    <p id="GFG_UP" style="font-size: 15px;  
                          font-weight: bold;"> 
    </p> 
  
    <button onclick="GFG_Fun()"> 
        click here 
    </button> 
  
    <p id="GFG_DOWN" style="color:green;  
                            font-size: 20px;  
                            font-weight: bold;"> 
    </p> 
  
    <script> 
        var up = document.getElementById('GFG_UP');     
        up.innerHTML = "Click on the button to override" 
                    + " the function."; 
          
        var down = document.getElementById('GFG_DOWN'); 
          
        function Fun() { 
            return "This is from old function"; 
        } 
          
        down.innerHTML = Fun(); 
          
        function GFG_Fun() { 
            var newFun = Fun; 
            Fun = function() { 
                return "This is from overridden function"; 
            } 
            down.innerHTML = Fun(); 
        } 
    </script> 
</body>

输出:

如何覆盖JavaScript函数

示例2: 在这个示例中，使用上述方法覆盖了一个 parseFloat 方法。

<body style="text-align:center;"> 
  
    <h1 style="color:green;" id="h1"> 
        GeeksForGeeks 
    </h1> 
  
    <p id="GFG_UP" style="font-size: 15px;  
                          font-weight: bold;"> 
    </p> 
  
    <button onclick="GFG_Fun()"> 
        click here 
    </button> 
  
    <p id="GFG_DOWN" style="color:green;  
                            font-size: 20px;  
                            font-weight: bold;"> 
    </p> 
  
    <script> 
        var up = document.getElementById('GFG_UP');     
          
        up.innerHTML = "Click on the button to override" 
                    + " the function."; 
          
        var down = document.getElementById('GFG_DOWN'); 
          
        down.innerHTML = "Floor value of '2.345' is "; 
          
        function GFG_Fun() { 
              
            // Override 
            parseFloat = function(x) { 
                return "Floor value of '2.345' is " 
                            + Math.floor(x); 
            } 
              
            // Overriding the parseFloat function and 
            // use it as Math.floor 
            down.innerHTML = parseFloat(2.345); 
        } 
    </script> 
</body>

输出:

如何覆盖JavaScript函数