Function to check for balanced parenthesis in any string using Array.prototype.reduce(). Inspiration: https://medium.freecodecamp.org/check-out-these-useful-ecmascript-2015-es6-tips-and-tricks-6db105590377

balancedParanthesis.js

const isBalanced = str => {
  const arr = str.split('');
  const res = arr.reduce((acc, item) => {
    if ( acc.slice(-1)[0] === '(' ) {
      if ( item === ')' ) {
        acc.pop();
        return acc;
      }
    }
    if ( item === '(' || item === ')' ) {
      acc.push(item);
    }
    return acc;
  }, []);
  return res.length ? false : true;
}