Balanced Parens

balanced-parens.js

module.exports = function checkBal(input) {
  function match(left, right) {
      return left === '(' && right === ')';
  }
  function removeLast(ar) {
      return ar.slice(0, ar.length - 1);
  }
  var result = input.split('').reduce(function(prev, curr, index, array) {
    if (!prev.length) return [curr];
    if (match(prev[prev.length -1], curr)) return removeLast(prev);
    return prev.concat(curr);
  }, []);
  
  return result.length === 0;
}