If objects are key value pairs, how can functions be objects in javascript

Question

If all functions in JS are objects, and objects are just collections of key:value pairs - how do complex functions become objects? Say a function thats taking a param number, doing complex calculations on it and returning the result - how is that an object? How do you store it as key/value pairs?

Answer 1

Objects are collections of key-value pairs indeed, but they are not just so.

Think of this ability as an interface: given a JavaScript object, you are guaranteed to be able to access its members (or elements) via a syntax of obj.foo or a obj['foo']. But at the same time, they can also have other abilities. Functions, in this case, is an example that can be called by a fn() syntax.

In fact, TypeScript allows you to declare a type that can do more than just key-value pairs:

type Type = {
    'foo': RegExp;  // a directly guaranteed member
    [number]: string;  // a rule-based convention:
                       // you can always get a string by a numeric index
                       // (or undefined)
    Method(): number;  // member function
    get children: HTMLElement[];  // getter/setter
    { new(): SomeClass };  // constructor of certain type
};