How to override a JavaScript function ?
Last Updated :
26 Dec, 2022
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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.
<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.
<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:
