function makeFunctionChainable(functionInstance) {
    return function() {
      for (var _len = arguments.length, args = new Array(_len), _key = 0; _key < _len; _key++) {
        args[_key] = arguments[_key];
      }

      var result = functionInstance.apply(void 0, [this._wrappedValue].concat(args));

      if (this._explicitChain || typeof result === 'string') {
        return new ChainWrapper(result, this._explicitChain);
      } else {
        return result;
      }
    };
  }
Make a voca function chainable.

@ignore
@param  {Function} functionInstance The function to make chainable
@return {Function}                  Returns the chainable function