JS functions first class objects

In JavaScript, functions are considered to be first-class objects. This means that they can be treated just like any other data type, such as strings, numbers, or arrays.

For example, just like you can assign a string to a variable, you can also assign a function to a variable. And just like you can pass a string to a function as an argument, you can also pass a function to another function as an argument.

Functions can also be returned from other functions, just like any other data type can be. This allows for a lot of flexibility in terms of how functions can be used and manipulated.

In short, first-class objects in JavaScript are objects that can be treated like any other object, and functions are just one type of first-class object in JavaScript.

// Define a simple arrow function
const greet = (name) => `Hello, ${name}`;

// Assign the function to a variable
const greeting = greet;

// Use the variable to call the function
console.log(greeting("John")); // Output: "Hello, John"

// Pass the function as an argument to another arrow function
const logGreeting = (fn) => console.log(fn("Jane"));

logGreeting(greet); // Output: "Hello, Jane"

ELI5

Ok, let’s imagine you have some toys to play with. Some of these toys are cars, some are balls and others are building blocks.

Just like you can play with cars and balls, you can also play with functions in JavaScript. Functions in JavaScript are just like any other toy, they can be passed around, stored in variables and even given as gifts to other functions.

That means functions in JavaScript are special toys called “first class objects”. It’s just like how cars and balls are first class toys that you can play with.

So when you have a function in JavaScript, you can treat it just like you would a car or a ball, you can play with it and give it to other functions to play with too.