Implement basic regex.

regex.js

function regex(p, s) {

  var pPointer = 0;
  var pLength = p.length;
  var pChar = '';
  var sPointer = 0;
  var sLength = s.length;
  var sChar = '';
  var wChar = '';

  for (; sPointer < sLength; ++sPointer) {

    sChar = s[sPointer];
    pChar = p[pPointer];

    if (pChar === '*' && sChar !== wChar) {      
      pPointer++;
      if (pPointer === pLength) {
        return true;
      }
      pChar = p[pPointer];
      wChar = '';
    } 

    if (sChar === pChar || pChar === '.' || pChar === '*') {
      pPointer++;
      wChar = sChar;
    } else {
      pPointer = 0;
    }

    if (pPointer === pLength) {
      return true;
    }
  }

  return false;
}

console.assert(regex('abb', 'abb'));
console.assert(regex('a*b', 'ab'));
console.assert(regex('a*b', 'aab'));
console.assert(regex('a*b', 'aaaab'));
console.assert(regex('a.b', 'aab'));
console.assert(regex('a.b', 'abb'));
console.assert(regex('a.b', 'acb'));
console.assert(!regex('cab', 'acb'));
console.assert(regex('ass', 'massage'));
console.assert(regex('a*', 'massage'), 'a*');
console.assert(regex('mas*age', 'massage'));
console.assert(regex('m..*age', 'massage'));
console.assert(regex('.*e', 'massage'));