JavaScript Strings

const a = 'single quotes';
const b = "double quotes";
const c = `backtick (template literal)`;

// Length
console.log("hello".length);  // 5

// Character access (zero-indexed)
const str = "JavaScript";
console.log(str[0]);          // "J"
console.log(str[4]);          // "S"
console.log(str.at(-1));      // "t" (last char - ES2022)
console.log(str.at(-2));      // "p"

// Escape sequences
const quote  = "She said \"hello\"";    // escaped double quote
const path   = 'C:\\Users\\Alice';       // escaped backslash
const newline = "Line 1\nLine 2";        // \n = newline
const tab    = "col1\tcol2";             // \t = tab

// String concatenation
const first = "John";
const last  = "Doe";
console.log(first + " " + last);   // "John Doe"
console.log(first.concat(" ", last)); // "John Doe"

const name = "Alice";
const age  = 30;

// Interpolation - any expression inside ${}
console.log(`Hello, ${name}!`);               // "Hello, Alice!"
console.log(`${name} is ${age} years old.`);  // "Alice is 30 years old."
console.log(`2 + 2 = ${2 + 2}`);              // "2 + 2 = 4"
console.log(`Upper: ${name.toUpperCase()}`);  // "Upper: ALICE"

// Ternary inside template
const isAdmin = true;
console.log(`Role: ${isAdmin ? "Admin" : "User"}`); // "Role: Admin"

// Multiline strings (preserves actual newlines)
const html = `
    <div class="card">
        <h2>${name}</h2>
        <p>Age: ${age}</p>
    </div>
`;

// Nested template literals
const items = ["apple", "banana", "cherry"];
const list = `Items: ${items.map(item => `[${item}]`).join(", ")}`;
console.log(list); // "Items: [apple], [banana], [cherry]"

const str = "Hello, World!";

// slice(start, end) - preferred substring method
console.log(str.slice(7));       // "World!" (from index 7 to end)
console.log(str.slice(7, 12));   // "World" (index 7 up to, not including, 12)
console.log(str.slice(-6));      // "World!" (from 6th from end)
console.log(str.slice(-6, -1));  // "World"  (negative end)

// toUpperCase / toLowerCase
console.log(str.toUpperCase());  // "HELLO, WORLD!"
console.log(str.toLowerCase());  // "hello, world!"

// trim - remove leading/trailing whitespace
const padded = "   hello   ";
console.log(padded.trim());      // "hello"
console.log(padded.trimStart()); // "hello   "
console.log(padded.trimEnd());   // "   hello"

// repeat
console.log("ha".repeat(3));    // "hahaha"

// padStart / padEnd - pad to a minimum length
console.log("5".padStart(3, "0")); // "005" (useful for IDs, time formatting)
console.log("hi".padEnd(10, "."));  // "hi........"

const text = "JavaScript is awesome and JavaScript is fun";

// includes - boolean check (preferred for existence check)
console.log(text.includes("awesome"));   // true
console.log(text.includes("python"));    // false
console.log(text.includes("Java", 15));  // true (search from index 15)

// startsWith / endsWith
console.log(text.startsWith("Java"));    // true
console.log(text.endsWith("fun"));       // true
console.log(text.startsWith("awesome", 14)); // true (from index 14)

// indexOf / lastIndexOf - return position or -1
console.log(text.indexOf("JavaScript"));     // 0 (first occurrence)
console.log(text.lastIndexOf("JavaScript")); // 26 (last occurrence)
console.log(text.indexOf("Python"));         // -1 (not found)

// search - like indexOf but accepts RegExp
console.log(text.search(/java/i));   // 0 (case-insensitive match)

// match - extract matches
const matches = text.match(/JavaScript/g); // global flag = all matches
console.log(matches); // ["JavaScript", "JavaScript"]

const dateStr = "2024-01-15";
const dateParts = dateStr.match(/(\d{4})-(\d{2})-(\d{2})/);
console.log(dateParts[1]); // "2024"
console.log(dateParts[2]); // "01"

// replace - replaces first match
const str = "cats are great, cats are cute";
console.log(str.replace("cats", "dogs")); // "dogs are great, cats are cute"

// replaceAll - replaces all matches (ES2021)
console.log(str.replaceAll("cats", "dogs")); // "dogs are great, dogs are cute"

// replace with function
const result = "hello world".replace(/\b\w/g, char => char.toUpperCase());
console.log(result); // "Hello World" (title case)

// String.fromCharCode / charCodeAt
console.log("A".charCodeAt(0));      // 65
console.log(String.fromCharCode(65)); // "A"

// Number formatting with strings
const price = 1234567.89;
console.log(price.toFixed(2));             // "1234567.89"
console.log(price.toLocaleString("en-US")); // "1,234,567.89"

// at() method (ES2022) - cleaner than length-based access
const arr = "Hello";
console.log(arr.at(0));  // "H"
console.log(arr.at(-1)); // "o"

// split - string to array
const csv = "apple,banana,cherry";
const fruits = csv.split(",");
console.log(fruits); // ["apple", "banana", "cherry"]

const words = "hello world foo".split(" ");
console.log(words);  // ["hello", "world", "foo"]

const chars = "abc".split("");
console.log(chars);  // ["a", "b", "c"]

// split with limit
console.log("a,b,c,d".split(",", 2)); // ["a", "b"]

// join - array to string
console.log(fruits.join(" - "));  // "apple - banana - cherry"
console.log(fruits.join(""));     // "applebananacherry"
console.log(fruits.join());       // "apple,banana,cherry" (default comma)

// Common pattern: reverse a string
const reversed = "hello".split("").reverse().join("");
console.log(reversed); // "olleh"

// Practical: parse a URL path
const path = "/api/users/42";
const parts = path.split("/").filter(Boolean); // filter removes empty strings
console.log(parts); // ["api", "users", "42"]

let greeting = "hello";

// Attempting to modify in place - silently does nothing
greeting[0] = "H";
console.log(greeting); // "hello" - unchanged!

// All methods return new strings
const upper = greeting.toUpperCase();
console.log(greeting); // "hello"   - original unchanged
console.log(upper);    // "HELLO"   - new string

// You must reassign if you want the changed value
greeting = greeting.toUpperCase();
console.log(greeting); // "HELLO"

// Chaining methods (each returns a new string)
const cleaned = "  Hello, World!  "
    .trim()
    .toLowerCase()
    .replace("hello", "hi");
console.log(cleaned); // "hi, world!"