Question

I am a self taught web developer and am still trying to come to grips with some JavaScript fundamentals. Below are some quotes extracted from Douglas Crockford’s Good Parts.

“Functions in JavaScript are Objects”

“In JavaScript, arrays are objects, functions are objects, regular expressions are objects, and, of course, objects are objects”

“Every object is linked to a prototype object from which it can inherit properties” (namely constructor, toString, …)

If Function is an Object then why

 console.log(typeof Function);  // function 

is its type a function and not object

 console.log(Object.constructor);  // Function()

is it the constructor of its ‘parent’

 console.log(Function.constructor);  // Function()

puzzled so the constructor is in-fact a function?

 console.log(typeof Function.prototype); // Function

is the type of its prototype a function and not an object? i thought it inherited from Object

Answers to these questions will greatly assist my understanding on JavaScript.

Answer 1

If Function is an Object then why is its type a function and not object?

Because the typeof operator is defined like that, probably for usability:

• Object (native and does not implement [[Call]]) returns "object"
• Object (native or host and does implement [[Call]]) returns "function"
• Object (host and does not implement [[Call]])
  returns an Implementation-defined value that may not be "undefined", "boolean", "number", or "string".

[[Call]] is an internal property of an object that identifies the object as a function (callable). A non-native object is an object provided by the host (e.g. browser), such as a DOM object or an instance of ActiveXObject.

puzzled so the constructor is in-fact a function?

Why wouldn’t it be? Constructors are functions. Instances can only be constructed using functions. Object.constructor is a function, but it’s also an object. See the following:

console.log((function () { }) instanceof Object);
//-> true

Also, from the ECMAScript speficiation:

Every built-in function and every built-in constructor has the Function prototype object, which is the initial value of the expression Function.prototype (15.3.4), as the value of its [[Prototype]] internal property.

Unless otherwise specified every built-in prototype object has the Object prototype object, which is the initial value of the expression Object.prototype (15.2.4), as the value of its [[Prototype]] internal property, except the Object prototype object itself.

And also, to answer your final puzzlement:

The Function prototype object is itself a Function object (its [[Class]] is "Function") that, when invoked, accepts any arguments and returns undefined.