String Methods and Template Literals

// Three ways to create strings
let single = 'Hello';
let double = "Hello";
let template = `Hello`;

// All three work the same for simple strings
console.log(single);   // Hello
console.log(double);   // Hello
console.log(template); // Hello

let message = "Hello";

// This doesn't change the original string
message.toUpperCase();
console.log(message);  // Still "Hello"

// You must save the result to use it
let upperMessage = message.toUpperCase();
console.log(upperMessage);  // "HELLO"

// Or reassign
message = message.toUpperCase();
console.log(message);  // "HELLO"

let name = "Alice";
let age = 25;

// Old way (concatenation)
let message1 = "Hello, my name is " + name + " and I'm " + age + " years old.";

// Modern way (template literal)
let message2 = `Hello, my name is ${name} and I'm ${age} years old.`;

console.log(message1);  // Hello, my name is Alice and I'm 25 years old.
console.log(message2);  // Hello, my name is Alice and I'm 25 years old.

let price = 50;
let quantity = 3;

// Calculations inside template literals
let total = `Total: $${price * quantity}`;
console.log(total);  // Total: $150

// Function calls
let greeting = `Hello, ${name.toUpperCase()}!`;
console.log(greeting);  // Hello, ALICE!

// Conditional expressions
let age = 20;
let status = `You are ${age >= 18 ? 'an adult' : 'a minor'}`;
console.log(status);  // You are an adult

// Old way (needs \n)
let oldPoem = "Roses are red\nViolets are blue\nJavaScript is awesome\nAnd so are you";

// Modern way (natural line breaks)
let newPoem = `
Roses are red
Violets are blue
JavaScript is awesome
And so are you
`;

console.log(newPoem);

let message = "Hello, World!";
console.log(message.length);  // 13

let empty = "";
console.log(empty.length);  // 0

let spaces = "   ";
console.log(spaces.length);  // 3 (spaces count!)

// Useful for validation
let password = "abc123";
if (password.length < 8) {
  console.log("Password too short! Minimum 8 characters.");
}

let text = "JavaScript";

// Using bracket notation (like arrays)
console.log(text[0]);  // J
console.log(text[4]);  // S
console.log(text[9]);  // t

// Using charAt() method
console.log(text.charAt(0));  // J
console.log(text.charAt(4));  // S

// Out of bounds
console.log(text[100]);       // undefined
console.log(text.charAt(100)); // "" (empty string)

// Last character
let lastIndex = text.length - 1;
console.log(text[lastIndex]);  // t

let text = "Hello World";

// Convert to uppercase
console.log(text.toUpperCase());  // HELLO WORLD

// Convert to lowercase
console.log(text.toLowerCase());  // hello world

// Original string unchanged
console.log(text);  // Hello World

// Common use: case-insensitive comparison
let input = "JAVASCRIPT";
let target = "javascript";

if (input.toLowerCase() === target.toLowerCase()) {
  console.log("Match!"); // This will execute
}

// Email validation (emails are case-insensitive)
let email = "User@Example.COM";
let normalizedEmail = email.toLowerCase();
console.log(normalizedEmail);  // user@example.com

// Display names
let firstName = "john";
let capitalized = firstName.charAt(0).toUpperCase() + firstName.slice(1);
console.log(capitalized);  // John

// Acronyms
let title = "hypertext markup language";
let acronym = title.split(" ")
  .map(word => word[0].toUpperCase())
  .join("");
console.log(acronym);  // HTML

let message = "JavaScript is awesome!";

// Check if string contains a word
console.log(message.includes("JavaScript"));  // true
console.log(message.includes("Python"));      // false

// Case-sensitive!
console.log(message.includes("javascript"));  // false

// Case-insensitive check
let search = "AWESOME";
console.log(message.toLowerCase().includes(search.toLowerCase()));  // true

// Practical use
let comment = "This is spam and fake";
if (comment.includes("spam") || comment.includes("fake")) {
  console.log("Comment flagged!");
}

let filename = "document.pdf";

// Check how string starts
console.log(filename.startsWith("doc"));  // true
console.log(filename.startsWith("Doc"));  // false

// Check how string ends
console.log(filename.endsWith(".pdf"));   // true
console.log(filename.endsWith(".txt"));   // false

// Practical: file type validation
if (filename.endsWith(".pdf") || filename.endsWith(".doc")) {
  console.log("Valid document format");
}

// URL validation
let url = "https://example.com";
if (url.startsWith("https://")) {
  console.log("Secure URL");
}

let text = "Hello World, Hello Universe";

// Find first occurrence
console.log(text.indexOf("Hello"));       // 0
console.log(text.indexOf("World"));       // 6
console.log(text.indexOf("Goodbye"));     // -1 (not found)

// Find last occurrence
console.log(text.lastIndexOf("Hello"));   // 13

// Check if substring exists
if (text.indexOf("World") !== -1) {
  console.log("Found 'World'");
}

// Modern alternative (cleaner)
if (text.includes("World")) {
  console.log("Found 'World'");
}

let text = "JavaScript";

// slice(start, end)
console.log(text.slice(0, 4));   // Java
console.log(text.slice(4));      // Script (from 4 to end)
console.log(text.slice(4, 10));  // Script

// Negative indices (count from end)
console.log(text.slice(-6));     // Script (last 6 characters)
console.log(text.slice(-6, -2)); // Scri

// Get last 3 characters
console.log(text.slice(-3));     // ipt

let text = "JavaScript";

// substring(start, end)
console.log(text.substring(0, 4));  // Java
console.log(text.substring(4));     // Script

// Note: substring doesn't support negative indices
console.log(text.substring(-3));    // JavaScript (treats -3 as 0)

// slice is generally preferred over substring

// Extract domain from email
let email = "user@example.com";
let atIndex = email.indexOf("@");
let domain = email.slice(atIndex + 1);
console.log(domain);  // example.com

// Get file extension
let filename = "document.pdf";
let dotIndex = filename.lastIndexOf(".");
let extension = filename.slice(dotIndex);
console.log(extension);  // .pdf

// Truncate long text
let longText = "This is a very long text that needs to be shortened";
let preview = longText.slice(0, 20) + "...";
console.log(preview);  // This is a very long...

let text = "   Hello World   ";

// Remove whitespace from both ends
console.log(text.trim());       // "Hello World"

// Remove from start only
console.log(text.trimStart());  // "Hello World   "

// Remove from end only
console.log(text.trimEnd());    // "   Hello World"

// Practical: clean user input
let userInput = "  john@example.com  ";
let cleanEmail = userInput.trim().toLowerCase();
console.log(cleanEmail);  // "john@example.com"

let text = "Hello World, Hello Universe";

// Replace first occurrence
console.log(text.replace("Hello", "Hi"));  // Hi World, Hello Universe

// Replace all occurrences (ES2021)
console.log(text.replaceAll("Hello", "Hi"));  // Hi World, Hi Universe

// Case-insensitive replace with regex
let message = "JavaScript is GREAT! JavaScript rocks!";
let newMessage = message.replace(/javascript/gi, "JS");
console.log(newMessage);  // JS is GREAT! JS rocks!

// Practical: clean up text
let dirty = "This    has    extra    spaces";
let clean = dirty.replace(/\s+/g, " ");
console.log(clean);  // This has extra spaces

let star = "*";

// Repeat a string
console.log(star.repeat(5));  // *****

// Create patterns
let line = "-".repeat(20);
console.log(line);  // --------------------

// Indentation
let indent = " ".repeat(4);
console.log(indent + "Indented text");

// Loading indicator
for (let i = 1; i <= 3; i++) {
  console.log("Loading" + ".".repeat(i));
}
// Loading.
// Loading..
// Loading...

let sentence = "JavaScript is awesome";

// Split into words
let words = sentence.split(" ");
console.log(words);  // ["JavaScript", "is", "awesome"]

// Split into characters
let text = "Hello";
let chars = text.split("");
console.log(chars);  // ["H", "e", "l", "l", "o"]

// Split by comma
let csv = "apple,banana,orange";
let fruits = csv.split(",");
console.log(fruits);  // ["apple", "banana", "orange"]

// Limit number of splits
let limited = sentence.split(" ", 2);
console.log(limited);  // ["JavaScript", "is"]

let words = ["JavaScript", "is", "awesome"];

// Join with space
console.log(words.join(" "));   // JavaScript is awesome

// Join with comma
console.log(words.join(","));   // JavaScript,is,awesome

// Join with nothing
console.log(words.join(""));    // JavaScriptisawesome

// Join with custom separator
console.log(words.join(" - ")); // JavaScript - is - awesome

// Reverse a string
let text = "JavaScript";
let reversed = text.split("").reverse().join("");
console.log(reversed);  // tpircSavaJ

// Count words
let sentence = "The quick brown fox jumps";
let wordCount = sentence.split(" ").length;
console.log(wordCount);  // 5

// Create initials
let fullName = "John Michael Doe";
let initials = fullName
  .split(" ")
  .map(word => word[0])
  .join("");
console.log(initials);  // JMD

// Format phone number
let digits = "1234567890";
let formatted = digits.split("").join("-");
console.log(formatted);  // 1-2-3-4-5-6-7-8-9-0

// Better phone format
let phone = "1234567890";
let parts = [phone.slice(0,3), phone.slice(3,6), phone.slice(6)];
console.log(parts.join("-"));  // 123-456-7890

function validateUsername(username) {
  // Remove whitespace
  username = username.trim();
  
  // Check length
  if (username.length < 3) {
    return "Username too short (minimum 3 characters)";
  }
  
  if (username.length > 20) {
    return "Username too long (maximum 20 characters)";
  }
  
  // Check for spaces
  if (username.includes(" ")) {
    return "Username cannot contain spaces";
  }
  
  // Check for special characters (simple check)
  if (!/^[a-zA-Z0-9_]+$/.test(username)) {
    return "Username can only contain letters, numbers, and underscores";
  }
  
  return "Valid username!";
}

console.log(validateUsername("  john_doe  "));  // Valid username!
console.log(validateUsername("ab"));            // Username too short
console.log(validateUsername("john doe"));      // Username cannot contain spaces

function formatName(firstName, lastName) {
  // Clean and capitalize
  let first = firstName.trim().toLowerCase();
  let last = lastName.trim().toLowerCase();
  
  // Capitalize first letter
  first = first.charAt(0).toUpperCase() + first.slice(1);
  last = last.charAt(0).toUpperCase() + last.slice(1);
  
  return `${first} ${last}`;
}

console.log(formatName("  jOHN  ", "  dOE  "));  // John Doe

function createSlug(title) {
  return title
    .toLowerCase()
    .trim()
    .replace(/\s+/g, "-")      // Replace spaces with hyphens
    .replace(/[^a-z0-9-]/g, "") // Remove special characters
    .replace(/-+/g, "-");       // Replace multiple hyphens with single
}

console.log(createSlug("Hello World! How are you?"));  // hello-world-how-are-you

function parseEmail(email) {
  email = email.trim().toLowerCase();
  
  let atIndex = email.indexOf("@");
  
  if (atIndex === -1) {
    return { valid: false };
  }
  
  let username = email.slice(0, atIndex);
  let domain = email.slice(atIndex + 1);
  
  return {
    valid: true,
    username: username,
    domain: domain,
    fullEmail: email
  };
}

let result = parseEmail("  John.Doe@Example.COM  ");
console.log(result);
// {
//   valid: true,
//   username: "john.doe",
//   domain: "example.com",
//   fullEmail: "john.doe@example.com"
// }

let input = "  HELLO WORLD  ";

// Chain multiple methods
let result = input
  .trim()           // "HELLO WORLD"
  .toLowerCase()    // "hello world"
  .replace(" ", "-"); // "hello-world"

console.log(result);  // hello-world

// More complex chaining
let email = "  User@EXAMPLE.com  ";
let normalized = email.trim().toLowerCase();
console.log(normalized);  // user@example.com

// Processing user input
let userInput = "  JavaScript   is   AWESOME!  ";
let processed = userInput
  .trim()
  .replace(/\s+/g, " ")     // Normalize spaces
  .toLowerCase()
  .split(" ")
  .join("-");

console.log(processed);  // javascript-is-awesome!