AJAX and HTTP Overview

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Questions and Answers

What is the primary purpose of rendering in web development?

To prepare data for AJAX requests

To optimize search engine rankings

To execute JavaScript commands

To generate HTML markup for browser display (correct)

Which method of the XMLHttpRequest object establishes a connection to the server?

open (correct)

getResponseHeader

send

setRequestHeader

In the XMLHttpRequest open method, what does the 'Method' parameter represent?

The HTTP method to be used for the request (correct)

The data to be sent with the request

The URL to send the request to

The asynchronous nature of the request

What feature allows AJAX to update parts of a webpage without reloading it?

Partial page updates Signup and view all the answers

How does the asynchronous nature of AJAX affect JavaScript execution?

JavaScript continues executing without waiting for the server response Signup and view all the answers

When using the GET method in XMLHttpRequest, where should parameters be included?

In the URL of the request Signup and view all the answers

What must be done in XMLHttpRequest when using POST method regarding the request's content type?

Change the MIME type using setRequestHeader Signup and view all the answers

What is the function of the send method in the XMLHttpRequest object?

To send the actual request to the server Signup and view all the answers

What does HTTP stand for?

Hypertext Transfer Protocol Signup and view all the answers

What does it mean for HTTP to be a stateless protocol?

Each request is treated independently without retaining any prior information. Signup and view all the answers

What is the primary advantage of long polling over short polling?

It allows the server to send updates instantly when data becomes available. Signup and view all the answers

What happens when a new request is sent after the previous connection is closed?

A new connection is established. Signup and view all the answers

How does long polling reduce network overhead compared to short polling?

By allowing the server to respond only when there is new data. Signup and view all the answers

What is a potential downside of short polling?

It can increase network overhead with repeated requests. Signup and view all the answers

Which statement about HTTP requests is correct?

Each HTTP request is independent and contains all necessary data. Signup and view all the answers

What role does the client play in long polling?

It only sends one request and waits for the server to respond. Signup and view all the answers

What does the readyState property represent in an XMLHttpRequest object?

The current state of the request Signup and view all the answers

At which readyState value does the XMLHttpRequest object indicate that all data has been received?

4 Signup and view all the answers

What method is used to detect changes in the readyState of an XMLHttpRequest object?

onreadystatechange Signup and view all the answers

Which status code indicates a successful request from the server?

200 Signup and view all the answers

What information does the responseText property provide?

The response data in text format Signup and view all the answers

Study Notes

AJAX Overview

AJAX stands for Asynchronous JavaScript and XML
AJAX uses existing techniques to update web pages
Primarily dependent on XMLHttpRequest
Updates part of a page without reloading entire page
JavaScript execution continues without waiting for server response

HTTP Protocol

HTTP stands for Hypertext Transfer Protocol
Enables clients (like web browsers) and servers to share information
It's an application layer protocol
Used to transfer data across the web
When a request is sent to the server, a connection is established between client and server
The server receives the request, processes it and sends back the response, then the connection is closed
If another request is sent, it is treated as a new request, and a new connection is established
HTTP is a stateless protocol: the server forgets everything related to the client/browser state, each request is independent of the other

HTTP Long Polling

Traditional web browsers use a pull-based approach (short polling) to fetch data
Clients repeatedly send requests to check for updates, increasing network overhead
Servers process unnecessary requests even without new data to return
Long polling is a push-based approach
Server sends updates to the client as soon as available
HTTP connection enables the server to reply later when data becomes available or when a timeout threshold is reached
Clients only need to send one request, and initiate a new request to get the latest data

Rendering

Rendering is the process of generating HTML markup to display web pages in the browser
How, and where rendering happens can significantly affect user experience, site performance, and SEO

AJAX Functionality

AJAX is a collection of pre-existing techniques
XMLHttpRequest object is used to make requests to the server
XMLHttpRequest allows retrieving data in XML, JSON, HTML, and plain text
AJAX updates parts of a page without requiring full page reloads

AJAX with XMLHttpRequest

XMLHttpRequest is a JavaScript object (XHR)
Instantiate an XMLHttpRequest object: XHR = new XMLHttpRequest() to send requests
open() method to establish connection; specify the method and URL. Example - xhr.open("GET", "page.php", true)
The HTTP method (e.g., GET or POST) is specified. Use capital letters
send() method sends the request to the server
Use setRequestHeader() to specify the MIME type (e.g., Content-Type) to send data to the server. For POST requests, you usually need to set the content type this way:

xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");

aAsync defines if transfer is asynchronous or synchronous
readyState property indicates the state of the request:
- 0 : Request not initialized
- 1 : Server connection established
- 2 : Request received
- 3 : Processing request
- 4 : Request finished and response is ready
status property contains the HTTP response status code; 200 is a success code
responseText is a string containing the server response in plain text
responseXML is the returned response in XML format

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Description

This quiz explores the fundamentals of AJAX and the HTTP protocol. Learn how AJAX allows for asynchronous updates to web pages and how HTTP facilitates communication between clients and servers. Test your knowledge on these essential web technologies.