https://coderpad.io/369ZMHWR

balancedParens.js

var data = [
    "(if (zero? x) max (/ 1 x))",
    "I told him (that it's not (yet) done). (But he wasn't listening)",
    ":-)",
    "())(",
    "((d)o(n)e)",
    ")("
  ];

function isBalanced(chars) {

  var findMatch = (list, isBalanced, total) => {
    
    var b = !(!isBalanced || total < 0);

    if (!list.length) return b;
    else if (list[0] == '(') return findMatch(list.slice(1), b, total + 1);
    else if (list[0] == ')') return findMatch(list.slice(1), b, total - 1);
    else return findMatch(list.slice(1), b, total);
    
  }

  return findMatch(chars, true, 0);
}

/** TEST SUITE **/

var Mocha = require('mocha');
var expect = require('chai').expect;
var mocha = new Mocha({ui: 'bdd'});
mocha.suite.emit('pre-require', this, 'solution', mocha);

describe("Balanced parentheses", () => {
  
  var r = [true, true, false, false, true, false];
  
  data.forEach((str, i) => {
    it("should be " + (r[i] ? "balanced" : "unbalanced"), () => {
      var chars = str.split('');
      expect(isBalanced(chars)).to.equal(r[i]);
    }); 
  });
  
});

mocha.run(function() {});