In this article, we are given an HTML document and the task is to override the function, either a predefined function or a user-defined function using JavaScript.
Approach: When we run the script then Fun() function is called. After clicking the button the GFG_Fun() function is called and this function contains another function that will run.
Example 1: In this example, a function written by the user is overridden.
html
<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> |
Output:
Example 2: In this example, a parseFloat method is overridden using the above-mentioned approach.
html
<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> |
Output:
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