First-class Functions in Javascript

Introduction

First-class functions mean functions are treated like any other variable or value
A programming language is said to have First-class functions when functions in that language are treated like any other variable
A function can be passed as an argument to other functions
A function can be returned by another function and can be assigned as a value to a variable

Assign function to a variable:

In JavaScript, any functions can be assigned to a variable

//Example
const message = function () {
    console.log("message");
}
// Invoke it using the variable
message();

Pass a function as an Argument

In JavaScript, we can pass a function as an argument to another function

//Example:
function sayHello() {
  return "Hello, ";
}
function greeting(helloMessage, name) {
    console.log(helloMessage() + name);
}
// Pass `sayHello` as an argument to `greeting` function
greeting(sayHello, "JavaScript!");

Return a function

A function can return another function

unction sayHello() {
    return function () {
        console.log("Hello!");
    }
}