Function

as First-class Citizen

QUIZ

1r.nu/eventloop

First-class citizen

In programming language design, a first-class citizen (also object, entity, or value) in a given programming language is an entity which supports all the operations generally available to other entities. These operations typically include being passed as a parameter, returned from a function, and assigned to a variable.

In JavaScript, functions are first-class objects,

i.e. they are objects and can be manipulated and passed around just like any other object.

Specifically, they are Function objects.

Functions can

be stored in variable
have properties
be properties of Objects
be arguments to other functions
be returned by other functions

Assigning functions to a variable

function multiply(x, y) {
   return x * y;
}

var multiply = function(x, y) {
   return x * y;
};

var multiply = function func_name(x, y) {
   return x * y;
};

Function declaration

Function expression

Named function expression

var multiply = new Function("x","y","return x*y")

Function constructor

And that’s why functions are first class citizens in JavaScript :)