function validBraces(braces){
  var matches = { '(':')', '{':'}', '[':']' };
  var stack = [];
  var currentChar;

  for (var i = 0; i < braces.length; i++) {
    currentChar = braces[i];

    if (matches[currentChar]) { // opening braces
      stack.push(currentChar);
    } else { // closing braces
      if (currentChar !== matches[stack.pop()]) {
        return false;
      }
    }
  }

  return stack.length === 0; // any unclosed braces left?
}