Refactoring – Introduce Parameter Object

Refactoring Jun 16, 2022

Hi developer, in this small article I want to talk about one concept introduced by Martin Fowler in your amazing book Refactoring, Chapter 6.


Sometimes we faced a group of data organized together, appearing in one function and another. In this case, we could gather these data in a unique data structure.

According to the author, the true efficiency of this refactor is in the mode of how it allows modifications deeper in the code.


function getProfile(name, age, skills) {
  const skillsList = skills.split(",");
  return `Hey ${name}, your age is ${age}, your skills are: ${skillsList}`;

Now, we could create a class to pass into the function replacing all the parameters, it could be an object, but a class gives us the power to carry methods through the instance, giving to us more flexibility and power.

class Person {
  constructor(name, age, skills) {
    this._data = {
      name: name,
      age: age,
      skills: skills

  get name() {

  get age() {
    return this._data.age;

  get skills() {
    return this._data.skills;

First, we get a new instance of the class:

const oneGuy = new Person('Diogo', '30', ['React', 'Javascript']);

And then we to refactor the method:

export function getProfile(person) {
  const skillsList = person.skills.join(",");
  return `Hey ${}, your age is ${person.age}, your skills are: ${skillsList}`;

Replace the old call with the new class parameter:


As explained, one advantage of use class is we can bring methods to the instance turning the code more clear and powerful. I will create a method to abstract the resume into the class Person `resume()`:

// Person class
// ...
resume() {
    const skillsList = this._data.skills.join(",");
    return `Hey ${}, your age is ${this._data.age}, your skills are: ${skillsList}`

Finally, we can replace a bunch of code of `getProfile` and have a method more clear and easy to read:

export function getProfile(person) {
  return person.resume();

Try it using my CodeSandBox example 🚀