check for balanced parens

parentheses_check.js

function parenthesesAreBalanced(s)
{
  var parentheses = "[]{}()",
    stack = [], //Parentheses stack
    i, //Index in the string
    c; //Character in the string

  for (i = 0; c = s[i++];)
  {
    var bracePosition = parentheses.indexOf(c),
      braceType;
    //~ is truthy for any number but -1
    if (!~bracePosition)
      continue;

    braceType = bracePosition % 2 ? 'closed' : 'open';

    if (braceType === 'closed')
    {
      //If there's no open paren, return false OR if opening paren does not match.
      if (!stack.length || parentheses.indexOf(stack.pop()) != bracePosition - 1)
        return false;
    }
    else
    {
      stack.push(c);
    }
  }
  //If anything is left on the stack <- not balanced
  return !stack.length;
}


// OR, using RegEx...
function isBalanced(string) {
    return !!balanced.matches({source: string, open: ['{', '(', '['], close: ['}', ')', ']'], balance: true});
}


parenthesesAreBalanced('{}([])'); // true
parenthesesAreBalanced('{{');     // false

isBalanced('{}([])');             // true
isBalanced('{{');                 // false