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Passing a function as a parameter in JavaScript

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  • Last Updated : 26 Dec, 2022
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In this article, we will pass a function as a parameter in Javascript. Passing a function as an argument to the function is quite similar to passing a variable as an argument to the function. so variables can be returned from a function. 

The below examples describe passing a function as a parameter to another function. 

Example 1: This example passes a function geeks_inner to the function geeks_outer as an argument. 

html




<body style="text-align:center;">
    <h1 style="color:green;">
        GeeksForGeeks
    </h1>
  
    <p>
        Passing function as arguments.
    </p>
  
    <!-- Function call after clicking the button -->
    <button onclick="geeks_outer(geeks_inner)">
        Click Here
    </button>
  
    <script>
        function geeks_inner(value){
            return 'hello User!';
        }
        function geeks_outer(func){
            alert(func());
        }
    </script>
</body>

Output:

 

Example 2: This example passes a function geeks_inner along with an argument ‘Geeks!’ to the function geeks_outer as an argument. 

html




<body style="text-align:center;">
  
    <h1 style="color:green;">
        GeeksForGeeks
    </h1>
  
    <p>
        Passing function as arguments.
    </p>
  
    <button onclick="geeks_outer('Geeks!', geeks_inner)">
        Click Here
    </button>
  
    <!-- Script to uses function call using
            function as argument -->
    <script>
        function geeks_inner(value){
            return 'hello '+value;
        }
        function geeks_outer(a, func){
            alert(func(a));
                }        
    </script>
</body>

Output:

 

 Example 3: Here in this example, a smaller function is passed as an argument in the sayHello function. so here actually we are passing a smaller function address to the function sayHello.

Javascript




<script>
    function sayHello(param){
    console.log("hello",param);
    param();
    return "Hiii Geeks for Geeks"
    }
      
    //function address
    function smaller(){
    console.log("Is everything alright")
    }
          
    //function call
    const returnHello= sayHello(smaller)
    console.log(returnHello)
</script>

Output:

hello ƒ smaller(){
    console.log("Is everything alright")
    }
Is everything alright]
Hiii Geeks for Geeks

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