RegExp Built-ins

new RegExp(pattern: string | RegExp, flags?: string)

// From string pattern
const regex1 = new RegExp('\\d+');
const regex2 = new RegExp('hello', 'i');

// From regex literal
const regex3 = /\d+/g;
const regex4 = /hello/i;

// Copy with new flags
const regex5 = new RegExp(/abc/, 'gi');

const regex = /pattern/gimsu;
console.log(regex.flags);  // 'gimsu'
console.log(regex.global); // true
console.log(regex.ignoreCase); // true

const regex = /hello/i;
console.log(regex.source);  // 'hello'

const regex = /hello/gi;
console.log(regex.flags);  // 'gi'

const regex = /test/g;
console.log(regex.global);  // true

const regex = /test/i;
console.log(regex.ignoreCase);  // true

const regex = /test/m;
console.log(regex.multiline);  // true

const regex = /test/s;
console.log(regex.dotAll);  // true

const regex = /test/u;
console.log(regex.unicode);  // true

const regex = /test/y;
console.log(regex.sticky);  // true

const regex = /\d/g;
const str = 'a1b2c3';

regex.test(str);
console.log(regex.lastIndex);  // 2

regex.test(str);
console.log(regex.lastIndex);  // 4

regex.test(str: string): boolean

const regex = /\d+/;
console.log(regex.test('abc'));    // false
console.log(regex.test('abc123')); // true

// With global flag
const globalRegex = /\d/g;
const str = 'a1b2';
console.log(globalRegex.test(str));  // true (matches '1')
console.log(globalRegex.test(str));  // true (matches '2')
console.log(globalRegex.test(str));  // false (no more matches)

regex.exec(str: string): RegExpExecArray | null

const regex = /(\d+)-(\w+)/;
const result = regex.exec('ID: 123-abc');

console.log(result[0]);  // '123-abc' (full match)
console.log(result[1]);  // '123' (first group)
console.log(result[2]);  // 'abc' (second group)
console.log(result.index);  // 4 (match position)

// With global flag
const globalRegex = /\d/g;
const str = 'a1b2c3';

let match;
while ((match = globalRegex.exec(str)) !== null) {
  console.log(`Found ${match[0]} at index ${match.index}`);
}
// Found 1 at index 1
// Found 2 at index 3
// Found 3 at index 5

/[abc]/        // Match a, b, or c
/[^abc]/       // Match anything except a, b, c
/[a-z]/        // Match lowercase letters
/[0-9]/        // Match digits
/./            // Match any character (except newline without 's' flag)

/\d/    // Digit [0-9]
/\D/    // Non-digit [^0-9]
/\w/    // Word character [a-zA-Z0-9_]
/\W/    // Non-word character [^a-zA-Z0-9_]
/\s/    // Whitespace [ \t\n\r\f]
/\S/    // Non-whitespace [^ \t\n\r\f]

/a*/       // 0 or more
/a+/       // 1 or more
/a?/       // 0 or 1
/a{3}/     // Exactly 3
/a{2,5}/   // 2 to 5
/a{2,}/    // 2 or more

/^abc/     // Start of string (or line with 'm' flag)
/abc$/     // End of string (or line with 'm' flag)
/\b/       // Word boundary
/\B/       // Non-word boundary

/(abc)/           // Capturing group
/(?:abc)/         // Non-capturing group
/(?<name>abc)/    // Named capturing group

/cat|dog/         // Match 'cat' or 'dog'
/gr(a|e)y/        // Match 'gray' or 'grey'

/foo(?=bar)/      // Positive lookahead
/foo(?!bar)/      // Negative lookahead

/(\w+)\s\1/       // Match repeated words: 'test test'

function isValidEmail(email) {
  const regex = /^[a-zA-Z0-9._+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$/;
  return regex.test(email);
}

console.log(isValidEmail('[email protected]'));  // true
console.log(isValidEmail('invalid.email'));     // false

function extractNumbers(str) {
  const regex = /\d+/g;
  const matches = [];
  let match;
  
  while ((match = regex.exec(str)) !== null) {
    matches.push(parseInt(match[0]));
  }
  
  return matches;
}

console.log(extractNumbers('abc 123 def 456 xyz 789'));
// [123, 456, 789]

function slugify(text) {
  return text
    .toLowerCase()
    .replace(/[^a-z0-9]+/g, '-')
    .replace(/^-+|-+$/g, '');
}

console.log(slugify('Hello World!'));  // 'hello-world'
console.log(slugify('  Foo Bar  '));  // 'foo-bar'

function parseDate(dateStr) {
  const regex = /(\d{4})-(\d{2})-(\d{2})/;
  const match = regex.exec(dateStr);
  
  if (match) {
    return {
      year: parseInt(match[1]),
      month: parseInt(match[2]),
      day: parseInt(match[3])
    };
  }
  
  return null;
}

console.log(parseDate('2024-06-15'));
// { year: 2024, month: 6, day: 15 }

function parseURL(url) {
  const regex = /^(?<protocol>https?):\/\/(?<domain>[^/]+)(?<path>\/.*)?$/;
  const match = regex.exec(url);
  
  if (match && match.groups) {
    return match.groups;
  }
  
  return null;
}

console.log(parseURL('https://example.com/path'));
// { protocol: 'https', domain: 'example.com', path: '/path' }

const text = `
Line 1
Line 2
Line 3
`;

// Match line starts
const regex = /^Line/gm;
const matches = text.match(regex);
console.log(matches);  // ['Line', 'Line', 'Line']

const str = 'The year is 2024';

// String.match
console.log(str.match(/\d+/));  // ['2024']

// String.search
console.log(str.search(/\d+/));  // 12

// String.replace
console.log(str.replace(/\d+/, '2025'));  // 'The year is 2025'

// String.split
console.log('a,b,c'.split(/,/));  // ['a', 'b', 'c']

// Efficient pattern matching
const regex = /\d+/g;
const largeText = /* large string */;

const start = performance.now();
const matches = largeText.match(regex);
const time = performance.now() - start;

console.log(`Found ${matches.length} matches in ${time}ms`);