Notes - David Umoru

NB: I update this from time to time as I learn new things.

…

OBJECTS AND OBJECT CONSTRUCTORS

Object Literals:
- Objects in JavaScript can be created using object literals, which is a straightforward way to group related data and functions.
- Example: const person = { name: 'John', age: 30 };.
Dot and Bracket Notation:
- Access object properties using dot notation (person.name) or bracket notation (person['name']).
- Bracket notation is useful when property names are dynamic or not valid identifiers.
Object Constructors:
- Constructors are functions used to create multiple similar objects. They use the new keyword to instantiate objects.
- Example:
```
function Person(name, age) {
  this.name = name;
  this.age = age;
}
const john = new Person('John', 30);
```
Prototypes:
- JavaScript objects have a prototype, which is another object from which they inherit properties and methods.
- Methods defined on a constructor’s prototype are shared across all instances created by that constructor.
- Example:
```
Person.prototype.sayHello = function() {
  console.log(`Hello, my name is ${this.name}`);
};
```
Prototypal Inheritance:
- Objects can inherit properties and methods from other objects. This is the basis for prototypal inheritance in JavaScript, allowing for the creation of more complex object structures.
Benefits of Constructors and Prototypes:
- Using constructors and prototypes helps to avoid redundancy, manage memory efficiently, and organize code better by separating concerns.

…

FACTORY FUNCTIONS AND THE MODULE PATTERN

Factory Functions:

A function that returns an object.
Allows for the creation of multiple objects with similar properties and methods without using new keyword or constructors.

Example:

function createDog(name, breed) {
    return {
        name,
        breed,
        bark() {
            console.log(`${this.name} says woof!`);
        },
    };
}

Benefits of Factory Functions:
- Encapsulation: Keeps the object creation logic within the function.
- No need for new keyword, preventing common mistakes associated with it.

The Module Pattern:

A way to encapsulate private variables and expose public methods.
Useful for organizing code and creating modules.

Example:

const Counter = (() => {
    let count = 0; // private variable

    return {
        increment() {
            count++;
            console.log(count);
        },
        reset() {
            count = 0;
        },
    };
})();

Encapsulation:
- Protects private data and exposes only necessary parts of the module.
Real-World Application:
- Useful in building libraries, managing state, and organizing code in a clean manner.
Practical Applications:
- Use factory functions to create multiple instances of an object easily.
- Implement the module pattern to create namespaces in your code, reducing the likelihood of naming conflicts.
Example Scenarios:
- Creating a Library - Use factory functions for different book objects, and a module pattern to manage the library’s collection.
- Game Development - Use factory functions to create characters, and the module pattern to handle game states and logic.

…

ES6 MODULES

Before ES6 Modules: The Global Scope Problem

In pre-ES6 JavaScript, multiple scripts share the global scope.
- Example:
  - one.js: const greeting = "Hello, Odinite!";
  - two.js: console.log(greeting);
  - If one.js loads first, greeting is available globally; otherwise, errors occur.
Workaround using IIFE:
- Wrapping code in IIFE restricts variables to local scope:
```
(() => { const greeting = "Hello, Odinite!"; })();
```
- Only accessible values can be returned to global scope.

ES6 Modules (ESM)

Modules have private scope. You control what’s shared using export/import.
- Example of module isolation:
  one.js
```
const greeting = "Hello, Odinite!";
export { greeting };
```

Import and Export in ES6

Two types: Named Exports and Default Exports.

Named Exports:

Multiple exports possible:

export const greeting = "Hello!";
export const farewell = "Goodbye!";

Import using braces:

import { greeting, farewell } from './one.js';
console.log(greeting); // Hello!

Default Exports:

Only one default export per file.

Example:

export default "Hello, Odinite!";
// two.js
import greeting from './one.js';
console.log(greeting); // "Hello, Odinite!"

Default exports can be named anything upon import.

Mixing Named and Default Exports

You can have both types in one file.

Example:

export default "Hello, Odinite!";
export const farewell = "Goodbye!";

// two.js
import greeting, { farewell } from './one.js';
console.log(greeting, farewell); // "Hello, Odinite! Goodbye!"

Entry Points in ESM

Only one entry file needs to be linked in HTML:

<script type="module" src="main.js"></script>

Browser will load dependencies automatically.

CommonJS vs. ES6 Modules

CommonJS (CJS) used in Node.js (require/module.exports).
ESM natively supported in browsers; focus of modern JavaScript development.