W5. AJAX

Question 1

What does AJAX stand for?

Answer 1

Asynchronous Javascript And XML

Question 2

What is AJAX for?

Answer 2

Technique allowing clients to display active content requiring communication with server.
- without reloading page
- not necessarily asynchronous
- not necessarily XML
Also referred to as scripted HTML

Question 3

Process of AJAX communication between client and server

Answer 3

• Calls made to server from client for more info (may be in response to an event)
• when result of call is received from server, client updates contents of the page
  (better to use asynchronous code to reduce the delay of receiving info from server)

Question 4

When is AJAX a suitable technique to use?

Answer 4

Dynamic content
- page changes without being reloaded
Client-side computation dependent on data that is:
- too large to download to client in one go
- subject to frequent change

Question 5

What is an XMLHTTPRequest Object?

Answer 5

• corner stone of AJAX
• used to exchange data between browser and server
• permits parts of web page to be updated without reloading whole page

Question 6

What properties does a Response Object have?

Answer 6

• headers: response headers
• status - status code
• statusText - HTTP status code message
• ok - boolean for status between 200-299
• response body - ArrayBuffer, Blob/file, formData etc.

Question 7

What does CORS stand for?

Answer 7

Cross-Origin Resource Sharing

Question 8

CORS key points

Answer 8

• restricted by browsers for security reasons if initiated from scripts
• XMLHTTPRequest and fetch follow same-origin policy
• web app can only request resources from same origin app was loaded from (or other sources if response contains appropriate headers)
• if a page loaded from one web server wants to access another it must request permission from server