Understanding-JS

This repository is meant for study purposes only.

Some contents of this repository comes from the book Function JavaScript by Michael Fogus.

Table of Contents

• JavaScript's Multiple Paradigms
• First Class Functions

JavaScripts Multiple Paradigms

JavaScript is not strictly a functional programming language, instead it facilitates the use of other paradigms as well:

Functional programming

"Functional programming is the use of functions that transform values into units of abstraction, subsequently used to build software systems."

- Definition of an abstraction.
- The definition of an abstraction built from existing functions
- The use of said functions by other functions via parameter passing to achieve some behavior

Imperative programming

- Categorized by its attention no details.
- Built around direct manipulation and inspection of program state.
- Often restricted to a level of detail that is good for their compilers rather than for their programmers. (Sokolowski 1991).

This implementation describes a "99 Bottles of Beer" program and exactly a "99 Bottles of Beer" program. Imperative programs are often one-shot implementations and difficult to reuse.

  var lyrics = [];

  for (var bottles = 99; bottles > 0; bottles--) {
      lyrics.push(bottles + " bottles of beer on the wall");
      lyrics.push(bottles + " bottles of beer");
      lyrics.push("Take one down, pass it around");

      if (bottles > 1)
        lyrics.push((bottles - 1) + " bottles of beer on the wall.");
      else
        lyrics.push("No more bottles of beer on the wall!");
  }

Prototype-based object-oriented programming

Every object has a secret link to the object which created it, forming a chain. When an object is asked for a property that it does not have, its parent object is asked... continually up the chain until the property is found or until the root object is reached.

Each function in JavaScript (which are objects themselves) actually has a member called "prototype", which is responsible for providing values when an object is asked for them. Having this member allows the constructor mechanism to work. Adding a property to the prototype of a function object will make it available to the constructed object, as well as to all of the objects which inherit from it. ( http://stackoverflow.com/a/186279/1810241)

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First Class Functions

First Class Functions are functions that can go anywhere that any other value can go.

• A function can be stored in a variable.

    var hello = function() { return 'hello'; };
  
    hello(); // hello

• A function can be stored in an array slot.

    var hellos = ['hello', function() { return 'hello'; }];
  
    hellos[1](); // hello;

• A function can be stored in an object field.

    var hellos = {word: 'hello', fn: function() { return 'hello'; }};
  
    hellos.fn(); // hello;

• A function can be created as needed.

    (function() { return 'hello '; })() + 'world'; // hello world

• A function can be passed to a function.

    function sayHello(fn, msg) { return fn() + msg; }
  
    sayHello(function() { return 'hello '; }, 'world'); // hello world

• A function can be returned from a function.

    function sayHello() { return function() { return 'hello'; }}
  
    var greeting = sayHello();
    greeting(); // hello

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