AJAX and HTTP Overview

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Questions and Answers

What does the readyState property indicate in an XMLHttpRequest?

The format of the response received

The size of the data being sent

The current state of the XMLHttpRequest object (correct)

The response code from the server

At which readyState value is the XMLHttpRequest object fully received and ready to process?

4 (correct)

Which readiness state indicates that the XMLHttpRequest object has been created but not yet initialized?

0 (correct)

What function is executed when the readyState changes in XMLHttpRequest?

onreadystatechange Signup and view all the answers

Which status code indicates a successful request in the XMLHttpRequest?

200 Signup and view all the answers

What does rendering refer to in web development?

Generating HTML markup to display web pages in the browser. Signup and view all the answers

What is a primary purpose of AJAX?

To allow partial updates to a web page without a full reload. Signup and view all the answers

Which object is primarily used in AJAX for making requests?

XHR Signup and view all the answers

What does the 'open' method in XMLHttpRequest do?

Establishes a connection to prepare for the request. Signup and view all the answers

In AJAX, what does the 'send' method perform?

It sends the HTTP request to the server. Signup and view all the answers

What would you use the setRequestHeader method for?

To specify the content type of the request. Signup and view all the answers

What does the asynchronous nature of AJAX allow for?

The web page to update without freezing. Signup and view all the answers

Which HTTP method requires you to specify variables in the arguments of the send method?

POST Signup and view all the answers

What does HTTP stand for?

Hypertext Transfer Protocol Signup and view all the answers

Which of the following best describes the statefulness of HTTP?

HTTP is a stateless protocol requiring no session management. Signup and view all the answers

What is the main disadvantage of short polling compared to long polling?

Short polling can cause the server to process unnecessary requests. Signup and view all the answers

How does long polling improve efficiency in data retrieval?

It grants the server the ability to send updates as soon as they are available. Signup and view all the answers

What happens after a server processes a request sent by a client in HTTP?

The server returns a response and closes the connection. Signup and view all the answers

What is a significant feature of a stateless protocol like HTTP?

Each HTTP request must contain all necessary information. Signup and view all the answers

Which mechanism does HTTP lack that contributes to its stateless nature?

Session identification Signup and view all the answers

When using long polling, what occurs after the client receives the data from the server?

The client sends another new request for updates. Signup and view all the answers

Study Notes

AJAX Overview

AJAX stands for Asynchronous JavaScript and XML
It's a set of technologies used to update portions of a webpage without reloading the entire page
This is in contrast to traditional web pages that reload entirely for changes

HTTP Protocol

HTTP stands for Hypertext Transfer Protocol
It's an application layer protocol that enables client-server communication for data transfer on the web
HTTP is stateless, meaning the server doesn't retain information about previous client requests between connections

HTTP Protocol Function

When a client sends a request to a server, a connection is established
The server processes the request and sends back a response
After the server sends the response, the connection is closed.
If another request is made, it's treated as a new request and a new connection is created
HTTP is a stateless protocol, so each request is handled independently

Long Polling

Web browsers often use a pull-based approach (short polling), sending repeated requests to check for updates
This can increase network overhead
Long polling is a push-based system; the server sends updates to the client as soon as data becomes available
This method maintains an HTTP connection until data is available or a time-out occurs
It reduces network overhead and server processing load

Rendering

Rendering is the process of creating HTML markup to show web pages in the browser
How and where this rendering process occurs affects user experience, site performance, and SEO

AJAX Components

AJAX uses existing techniques, primarily XMLHttpRequest an object usable in JavaScript
XMLHttpRequest retrieves data in XML, JSON, HTML, or plain text formats via HTTP requests
It updates part of the page without needing a page reload

AJAX Use Case Example

AJAX can be used for suggestions and autocomplete like Google's search bar

AJAX Functioning Steps

Instantiate a XMLHttpRequest object
Establish a connection (using open) to the server
Send a request to the server
The open() method takes parameters (Method, Url, aSync)
- Method specifies the HTTP method (e.g., GET, POST)
- Url is the address of the server-side program
If using POST method, variables for the request must in the send parameter, and the request's MIME type should be set using setRequestHeader() method

AJAX State Tracking

The readyState property tracks the current state of the XMLHttpRequest object (0-4)
readyState is checked using an onreadystatechange event
When readyState is 4 and the status is 200, the server response is received
Error handling (status != 200) is crucial

Example JavaScript Code for AJAX

Code in example shows how to update a web element after receiving a response from the server

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Description

This quiz covers the fundamentals of AJAX and HTTP protocols. Learn about how AJAX allows for asynchronous updates on web pages and the stateless nature of HTTP. Test your knowledge on these essential web technologies and their functionalities.