code: function createChainedFunction(one, two) {
    var hasOne = typeof one === 'function';
    var hasTwo = typeof two === 'function';
  
    if (!hasOne && !hasTwo) {return null;}
    if (!hasOne) {return two;}
    if (!hasTwo) {return one;}
  
    return function chainedFunction() {
      one.apply(this, arguments);
      two.apply(this, arguments);
    };
  }
docs: Safe chained function
  
  Will only create a new function if needed,
  otherwise will pass back existing functions or null.
  
  @param {function} one
  @param {function} two
  @returns {function|null}