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How to add method to String class in JavaScript ?

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  • Difficulty Level : Easy
  • Last Updated : 05 Jan, 2023
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In this article, the task is to add a method to the String class in JavaScript. There are two approaches that are described with the proper examples: 

Approach 1: Use the Object.defineProperty() method, which is used to define a new property directly to an object, or modify an existing property. It takes 3 arguments, the first is Object, the Second is propertyName, and the last is propertyDescription. In this example, the sum of the length of strings is returned.

Example: This example uses the above-explained approach.

html




<body style="text-align: center">
    <h1 style="color: green">
        GeeksforGeeks
    </h1>
    <h3>
        Add method to String class in JavaScript
    </h3>
  
    <p id="GFG_UP"></p>
  
    <button onClick="GFG_Fun()">
        click here
    </button>
  
    <p id="GFG_DOWN"></p>
  
    <script>
        var up = document.getElementById('GFG_UP');
        var down = document.getElementById('GFG_DOWN');
          
        var str1 = "GeeksforGeeks";
        var str2 = "A Computer Science Portal";
          
        up.innerHTML = "Click on button to get the "
                    + "sum of length of the both "
                    + "strings<br>Str1 - '" + str1
                    + "'<br>Str2 - '" + str2 + "'";
          
        Object.defineProperty(String.prototype,
        'SumOfLength', {
            value: function(param) {
                return this.length + param.length;
            }
        });
          
        function GFG_Fun() {
            const res = str1.SumOfLength(str2);
            down.innerHTML = res;
        }
    </script>
</body>


Output:

 Add method to String class

 Add method to String class

Approach 2: Use String.prototype.propertyName to add a new method to the String class. Define a method that takes arguments passed by the object and performs the desired operation. In this example, the sum of the length of strings is returned.

Example: This example uses the above-explained approach.

html




<body style="text-align: center">
    <h1 style="color: green">GeeksforGeeks</h1>
    <h3>
        Add method to String
        class in JavaScript
    </h3>
  
    <p id="GFG_UP"></p>
  
    <button onClick="GFG_Fun()">
        click here
    </button>
  
    <p id="GFG_DOWN"></p>
  
    <script>
        var up = document.getElementById('GFG_UP');
        var down = document.getElementById('GFG_DOWN');
          
        var str1 = "GeeksforGeeks";
        var str2 = "A Computer Science Portal";
          
        up.innerHTML = "Click on button to get the "
                    + "sum of length of the both "
                    + "strings<br>Str1 - '" + str1
                    + "'<br>Str2 - '" + str2 + "'";
          
        String.prototype.SumOfLength = function( arg ) {
            return this.length + arg.length;
        };
        function GFG_Fun() {
            const res = str1.SumOfLength(str2);
            down.innerHTML = res;
        }
    </script>
</body>


Output:

 Add method to String class

 Add method to String class


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