What is a first class function

In JavaScript, first-class functions(first-class citizens) mean that functions are treated like any other variable. That means:

1. You can assign a function to a variable.
2. You can pass a function as an argument to another function.
3. You can return a function from another function.

This capability enables powerful patterns like callbacks, higher-order functions, event handling, and functional programming in JavaScript.

For example, the handler function below is assigned to a variable and then passed as an argument to the addEventListener method.

const handler = () => console.log("This is a click handler function");
document.addEventListener("click", handler);