JavaScript Fundamentals

javascript_fundamentals.js

//
// Console.log (output)
//

console.log("Basics ---------------------------------------");


//
// Comments
//
console.log();
console.log();
console.log("Comments ---------------------------------------");


// This is a comment
/*
This is a
multi-line comment
*/


//
// Primitives
//

console.log();
console.log();
console.log("Primitives ---------------------------------------");

// Number
console.log(typeof 4);

// Boolean
console.log(typeof true);

// String
console.log(typeof "David");

// Object
console.log(typeof {});

// Function
console.log(typeof function add() {});

// Null (object)
console.log(typeof null);

// undefined
console.log(typeof undefined);


//
// Variables and assignments
//

console.log();
console.log();
console.log("Assignments ---------------------------------------");

// var
var a;
console.log(a);

// let
let b = 5;
console.log(b);

// const
const c = 10;
console.log(10);

// Pass by value (primitives)
b = a;
console.log(b);
a = 10;
console.log(b);



//
// Arrays
//

console.log();
console.log();
console.log("Arrays ---------------------------------------");

// Create
a = [1, 2, 3];
console.log(a);

// Access
console.log(a[0]);
console.log(a[1]);
console.log(a[2]);

// Out of bounds access
console.log(a[3]);

// Assignment
a[3] = 4;
console.log(a[3]);



//
// Functions
//

console.log();
console.log();
console.log("Functions ---------------------------------------");

// Define a named functions
function hello() { return "Hello"; }

// Call/execute the function
console.log(hello());

// Assigning functions
a = function() { return "Hello"; }
console.log(a);
console.log(a());

// Multi-line functions
a = function() {
  let greeting = "Hello";
  return greeting;
}

// Anonymous, fat arrow declarations
a = () => { return "Hello"; }
console.log(a());

// Shortened syntax
a = () => "Hello";
console.log(a());

// Parameters
add = (x, y) => x + y;
console.log(add(2, 2));


//
// Lexical Scope
//

console.log();
console.log();
console.log("Lexical Scope ---------------------------------------");

// Functions can access surrounding context
a = 5
b = () => { return a; }
console.log(b());

// Functions can update surrounding context
b = () => {
  a = 10;
  return a;
}

console.log(b());
console.log(a);

// Functions can define their own scope/context
a = 5;
b = () => {
  let a = 10;
  return a;
}

console.log(b());
console.log(a);



//
// Objects (Dictionary)
//

console.log();
console.log();
console.log("Objects ---------------------------------------");

// Define an object with a key and value
a = { first: "David" }
console.log(a);

// Access the value
console.log(a.first);
console.log(a["first"]);

// Add a new key and value
a.last = "Raffauf";
console.log(a);