String Utilities

const capitalize = (str) => str.charAt(0).toUpperCase() + str.slice(1);

capitalize("hello world"); // "Hello world"
capitalize("javaScript");  // "JavaScript"

const capitalizeWords = (str) =>
  str.replace(/\b\w/g, (char) => char.toUpperCase());

capitalizeWords("hello world");        // "Hello World"
capitalizeWords("the quick brown fox"); // "The Quick Brown Fox"

const camelCase = (str) =>
  str
    .toLowerCase()
    .replace(/[^a-zA-Z0-9]+(.)/g, (_, char) => char.toUpperCase());

camelCase("hello world");      // "helloWorld"
camelCase("background-color"); // "backgroundColor"
camelCase("user_first_name");  // "userFirstName"

const kebabCase = (str) =>
  str
    .match(/[A-Z]{2,}(?=[A-Z][a-z]+\d*|\b)|[A-Z]?[a-z]+\d*|[A-Z]|\d+/g)
    .join("-")
    .toLowerCase();

kebabCase("helloWorld");       // "hello-world"
kebabCase("backgroundColor");  // "background-color"
kebabCase("HTMLParser");       // "html-parser"

const snakeCase = (str) =>
  str
    .match(/[A-Z]{2,}(?=[A-Z][a-z]+\d*|\b)|[A-Z]?[a-z]+\d*|[A-Z]|\d+/g)
    .join("_")
    .toLowerCase();

snakeCase("helloWorld");      // "hello_world"
snakeCase("backgroundColor"); // "background_color"
snakeCase("userFirstName");   // "user_first_name"

const slugify = (str) =>
  str
    .toLowerCase()
    .trim()
    .replace(/[^\w\s-]/g, "")
    .replace(/[\s_-]+/g, "-")
    .replace(/^-+|-+$/g, "");

slugify("Hello World!");         // "hello-world"
slugify("  The Quick Brown Fox") // "the-quick-brown-fox"
slugify("React & TypeScript");   // "react-typescript"

const truncate = (str, maxLength, suffix = "...") =>
  str.length > maxLength ? str.slice(0, maxLength - suffix.length) + suffix : str;

truncate("Hello, World!", 8);          // "Hello..."
truncate("Short", 10);                 // "Short"
truncate("Hello, World!", 8, " →");   // "Hello →"

const reverse = (str) => str.split("").reverse().join("");

reverse("hello"); // "olleh"
reverse("abcde"); // "edcba"

const isPalindrome = (str) => {
  const clean = str.toLowerCase().replace(/[^a-z0-9]/g, "");
  return clean === clean.split("").reverse().join("");
};

isPalindrome("racecar");         // true
isPalindrome("A man a plan a canal Panama"); // true
isPalindrome("hello");           // false

const countWords = (str) => str.trim().split(/\s+/).filter(Boolean).length;

countWords("Hello World");          // 2
countWords("  The quick brown fox") // 4
countWords("");                     // 0

const stripHtml = (str) => str.replace(/<[^>]*>/g, "");

stripHtml("<h1>Hello</h1> <p>World</p>"); // "Hello World"
stripHtml("<b>Bold</b> text");            // "Bold text"

// Pad a number with leading zeros
String(7).padStart(3, "0");  // "007"
String(42).padStart(5, "0"); // "00042"

// Pad with custom character
"hi".padEnd(5, ".");         // "hi..."
"hi".padStart(5, "-");       // "---hi"

const repeat = (str, n) => str.repeat(n);

repeat("ab", 3);  // "ababab"
repeat("ha", 4);  // "hahahaha"

const escapeHtml = (str) =>
  str
    .replace(/&/g, "&")
    .replace(/</g, "&lt;")
    .replace(/>/g, "&gt;")
    .replace(/"/g, "&quot;")
    .replace(/'/g, "&#039;");

escapeHtml('<script>alert("xss")</script>');
// "&lt;script&gt;alert(&quot;xss&quot;)&lt;/script&gt;"

const countOccurrences = (str, sub) =>
  str.split(sub).length - 1;

countOccurrences("hello world hello", "hello"); // 2
countOccurrences("aaaa", "aa");                 // 2