Passing a function as a parameter in JavaScript

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. 

function geeks_inner(value){
    return 'hello User!';
}
function geeks_outer(func){
    console.log(geeks_inner());
}

geeks_outer(geeks_inner);

hello User!

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

function geeks_inner(value) {
    return 'hello ' + value;
}
function geeks_outer(a, func) {
    console.log(func(a));
}

geeks_outer('Geeks!', geeks_inner);

hello Geeks!

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

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)

hello [Function: smaller]
Is everything alright
Hiii Geeks for Geeks