JavaScript

A Promise is in inbuilt JavaScript object which supports asynchronous handling of events via either a successful function or error function

// Success callback function success_callback(data) { ... } // Error callback function error_callback(message) { ... } // Define the promise var myPromise = new Promise(function(on_success,on_error)) { ... do something ... if (...positive case...) { on_success(...some data...); } else { on_error(...error message...); } ... perform cleanup ... }; // Invoke the promise myPromise.then( function(value) {success_callback(value);}, function(error) {error_callback(error);} );

A JavaScript Promise object has a State (Pending, Fulfilled, or Rejected) and a Result. Neither the State or the Result can be directly accessed from the Promise object, but the implementation of the Promise can assign the Result

Stateless : client state data is typically not stored on the server

Client <--> Server : Separation between client and server, supports isolation, independence, atomicity

Cache : Data can be cached on the client

URL Composition : data type and record identity is conveyed through the URL

HTTP verbs : GET, POST, PUT, DELETE used to perform CRUD

• GET - Read a record or get many records of a type
  • HTTP Response Code 200 (OK) on success
  • HTTP Response Code 404 (NOT FOUND) or 400 (Bad Request) on error
• POST - Add a record, or subordinate (child) records of another parent object
  • HTTP Response Code 201 on success, returning a location header with a link to the newly created resource.
• PUT - Update a record
  • On edit, HTTP Response Code 200 on success, or 204 if not returning content in body.
  • On create, HTTP Response Code 201 on success.
• DELETE - Remove a record
  • HTTP Response Code 200 (OK) on success, with response body
• PATCH - Modify a record, by sending only the changes in the request body (with instructions)
  • Use JSON patch or XML patch to describe in the body how a new resource will be created.

Fetch supports asynchronous data transmission over HTTP

fetch('http://example.com/movies.json') .then((response) => { return response.json(); }) .then((myJson) => { console.log(myJson); });

The fetch specification differs from jQuery.ajax() in three main ways:

1. The Promise returned from fetch() won’t reject on HTTP error status even if the response is an HTTP 404 or 500. Instead, it will resolve normally (with ok status set to false), and it will only reject on network failure or if anything prevented the request from completing.
2. fetch() won't receive cross-site cookies; you can’t establish a cross site session using fetch. Set-Cookie headers from other sites are silently ignored.
3. fetch won’t send cookies, unless you set the credentials init option. (Since Aug 25, 2017. The spec changed the default credentials policy to same-origin. Firefox changed since 61.0b13.)

// Example POST method implementation: async function postData(url = '', data = {}) { // Default options are marked with * const response = await fetch(url, { method: 'POST', // *GET, POST, PUT, DELETE, etc. mode: 'cors', // no-cors, *cors, same-origin cache: 'no-cache', // *default, no-cache, reload, force-cache, only-if-cached credentials: 'same-origin', // include, *same-origin, omit headers: { 'Content-Type': 'application/json' // 'Content-Type': 'application/x-www-form-urlencoded', }, redirect: 'follow', // manual, *follow, error referrerPolicy: 'no-referrer', // no-referrer, *client body: JSON.stringify(data) // body data type must match "Content-Type" header }); return await response.json(); // parses JSON response into native JavaScript objects } postData('https://example.com/answer', { answer: 42 }) .then((data) => { console.log(data); // JSON data parsed by `response.json()` call });

• Send a request with credentials
• Uploading a file
• Uploading JSON data
• Uploading multiple files
• Processing a text file line by line
• Checking that the fetch was successful
• Supplying your own request object