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 :)
