JavaScript Fundamentals

Variables and Data Types

1. Variable Declarations

// Modern variable declarations
let name = 'John'; // Block-scoped, mutable
const age = 30; // Block-scoped, immutable
var legacy = 'old'; // Function-scoped (avoid)

2. Primitive Data Types

// Numbers
const integer = 42;
const float = 3.14;
const scientific = 2.998e8;

// Strings
const single = 'Hello';
const double = 'World';
const template = `Hello ${name}`;

// Boolean
const isTrue = true;
const isFalse = false;

// Special Values
const empty = null;
const undefined_var = undefined;

3. Complex Data Types

// Arrays
const fruits = ['apple', 'banana', 'orange'];

// Objects
const person = {
  name: 'John',
  age: 30,
  greet() {
    return `Hello, I'm ${this.name}`;
  },
};

Control Structures

1. Conditionals

// if-else
if (age >= 18) {
  console.log('Adult');
} else {
  console.log('Minor');
}

// switch
switch (fruit) {
  case 'apple':
    console.log('Selected apple');
    break;
  default:
    console.log('Unknown fruit');
}

2. Loops

// for loop
for (let i = 0; i < 5; i++) {
  console.log(i);
}

// for...of (arrays)
for (const fruit of fruits) {
  console.log(fruit);
}

// for...in (objects)
for (const key in person) {
  console.log(`${key}: ${person[key]}`);
}

// while loop
let count = 0;
while (count < 5) {
  console.log(count++);
}

Functions

1. Function Declarations

// Regular function
function greet(name) {
  return `Hello, ${name}`;
}

// Arrow function
const greetArrow = (name) => `Hello, ${name}`;

// Function expression
const greetExpr = function (name) {
  return `Hello, ${name}`;
};

2. Parameters and Arguments

// Default parameters
function multiply(a, b = 1) {
  return a * b;
}

// Rest parameters
function sum(...numbers) {
  return numbers.reduce((total, num) => total + num, 0);
}

// Destructuring parameters
function printPerson({ name, age }) {
  console.log(`${name} is ${age} years old`);
}

Error Handling

1. Try-Catch

try {
  // Code that might throw an error
  throw new Error('Something went wrong');
} catch (error) {
  console.error(error.message);
} finally {
  // Always executed
  console.log('Cleanup');
}

2. Custom Errors

class ValidationError extends Error {
  constructor(message) {
    super(message);
    this.name = 'ValidationError';
  }
}

Best Practices

1. Code Style

• Use consistent indentation
• Follow naming conventions
• Keep functions small and focused
• Use meaningful variable names

2. Performance

• Avoid global variables
• Use appropriate data structures
• Optimize loops and conditions
• Minimize DOM manipulation

3. Debugging

• Use console methods effectively
• Implement proper error handling
• Write clear error messages
• Use debugging tools

Next Steps

1. Explore Core Concepts for advanced features
2. Learn about the JavaScript runtime environment
3. Practice with coding exercises and projects