如何覆盖 JavaScript函数？

给定一个 HTML 文档，任务是覆盖函数，无论是预定义函数还是使用 JavaScript 的用户定义函数。

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

示例 1：在此示例中，用户编写的函数被覆盖。

 
 
  
 
     
        How to override a JavaScript function ?
    

  
 
      
     
        GeeksForGeeks 
    
      
    
    
      
    
        click here
    
      
    
    
      
     
        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();
        }
     
 
  

输出：

• 在点击按钮之前：
  
• 点击按钮后：
  

示例 2：在此示例中， parseFloat方法被覆盖。

 
 
  
 
     
        How to override a JavaScript function ?
    

  
 
      
     
        GeeksForGeeks 
    
      
    
    
          
    
        click here
    
      
    
    
      
     
        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); 
        }
     
 
  

输出：

• 点击按钮前：
  
• 点击按钮后：