A reminder for functional programming in javascript.

Also, here is a good short comparison of functional and object-oriented programming.

ES6 Fetch API


Fetch API intro

This allows us to perform declarative HTTP requests to a server. For each request, it creates a Promise which must be resolved in order to define the content type and access the data.

The fetch() method returns a Promise that resolves the Response from the Request to show the status (successful or not). If you ever get this message promise {} in your console log screen, don’t panic — it basically means that the Promise works, but is waiting to be resolved. So in order to resolve it we need the .then() handler (callback) to access the content.

So in short, we first define the path (Fetch), secondly request data from the server (Request), thirdly define the content type (Body) and last but not least, we access the data (Response).

From Mozilla docs:

WindowOrWorkerGlobalScope is implemented by both Window and WorkerGlobalScope, which means that the fetch() method is available in pretty much any context in which you might want to fetch resources.

// Basic blueprint
  .then(response.something) // Define response type (JSON, Headers, Status codes)
  .then(data) // get the response type 

// Practical example
  .then(response => response.json())
  .then(data => console.log(data))

CRUD and other HTTP request methods

HTTP defines a set of request methods to indicate the desired action to be performed for a given resource. Although they can also be nouns, these request methods are sometimes referred to as HTTP verbs. Each of them implements a different semantic.

Main methods are:

  • POST (create a new resource)
  • GET
  • PUT (update resource – replaces all representations of current resource)
  • PATCH (partially update resource)

Other methods include HEAD, CONNECT, OPTIONS, TRACE

Creating a new user

// Create a new user
fetch('https://jsonplaceholder.typicode.com/users', {
  headers: { "Content-Type": "application/json; charset=utf-8" },
  method: 'POST',
  body: JSON.stringify({
    username: 'Elon Musk',
    email: 'elonmusk@gmail.com',

Deleting a user

// Create a new user
// we have to use the URL specific to that user (...users/1)
fetch('https://jsonplaceholder.typicode.com/users/1', {
  method: 'DELETE'

Updating a user

// Update user with id 3
fetch('https://jsonplaceholder.typicode.com/users/3', {
  headers: { "Content-Type": "application/json; charset=utf-8" },
  method: 'PUT',
  body: JSON.stringify({
    username: 'Elon Musk',
    email: 'elonmusk@gmail.com',

Observables and RXJS approach

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