/*
  Regular Expression
  Character Classes
  . => matches any character, except newline or other line terminators.
  w => matches word characters. [a-z, A-Z, 0-9 And Underscore]
  W => matches Non word characters
  d => matches digits from 0 to 9.
  D => matches non-digit characters.
  s => matches whitespace character.
  S => matches non whitespace character.
*/

let email = 'O@@@g...com O@g.com O@g.net A@Y.com O-g.com o@s.org 1@1.com';
let dot = /./g;
let word = /w/g;
let valid = /w@w.(com|net)/g;
console.log(email.match(dot));
console.log(email.match(word));
console.log(email.match(valid));