Javascript: Use reduce to check balanced parens

function balancedParens(str) {
    return !str.split('').reduce(function(previous, char){
    if (previous < 0) return previous;
    if (char == '(') previous++;
    if (char == ')') previous--;
    return previous;
  }, 0);
}

balancedParens('(sdfsdfsdf)')  // True
balancedParens('()()()()((()))') // True
balancedParens('())))(') // False
balancedParens('(())))(') // False
balancedParens(')(') // False

sunmingtao / sample-code

Javascript: Use reduce to check balanced parens #168