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?

  • 2
  • 4 (correct)
  • 1
  • 3

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

  • 1
  • 0 (correct)
  • 3
  • 2

What function is executed when the readyState changes in XMLHttpRequest?

<p>onreadystatechange (D)</p> Signup and view all the answers

Which status code indicates a successful request in the XMLHttpRequest?

<p>200 (A)</p> Signup and view all the answers

What does rendering refer to in web development?

<p>Generating HTML markup to display web pages in the browser. (B)</p> Signup and view all the answers

What is a primary purpose of AJAX?

<p>To allow partial updates to a web page without a full reload. (D)</p> Signup and view all the answers

Which object is primarily used in AJAX for making requests?

<p>XHR (D)</p> Signup and view all the answers

What does the 'open' method in XMLHttpRequest do?

<p>Establishes a connection to prepare for the request. (C)</p> Signup and view all the answers

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

<p>It sends the HTTP request to the server. (A)</p> Signup and view all the answers

What would you use the setRequestHeader method for?

<p>To specify the content type of the request. (B)</p> Signup and view all the answers

What does the asynchronous nature of AJAX allow for?

<p>The web page to update without freezing. (C)</p> Signup and view all the answers

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

<p>POST (A)</p> Signup and view all the answers

What does HTTP stand for?

<p>Hypertext Transfer Protocol (D)</p> Signup and view all the answers

Which of the following best describes the statefulness of HTTP?

<p>HTTP is a stateless protocol requiring no session management. (B)</p> Signup and view all the answers

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

<p>Short polling can cause the server to process unnecessary requests. (D)</p> Signup and view all the answers

How does long polling improve efficiency in data retrieval?

<p>It grants the server the ability to send updates as soon as they are available. (C)</p> Signup and view all the answers

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

<p>The server returns a response and closes the connection. (B)</p> Signup and view all the answers

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

<p>Each HTTP request must contain all necessary information. (A)</p> Signup and view all the answers

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

<p>Session identification (D)</p> Signup and view all the answers

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

<p>The client sends another new request for updates. (D)</p> Signup and view all the answers

Flashcards

What is HTTP?

HTTP stands for Hypertext Transfer Protocol, a protocol for transferring data across the World Wide Web.

What is a client in HTTP?

A client is a device or program that initiates requests for information from a server.

What is a server in HTTP?

A server is a device that stores web pages and files and responds to requests from clients.

Why is HTTP stateless?

HTTP is stateless because each request is treated independently. The server doesn't remember previous interactions.

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What is Long Polling?

Long polling is a technique where a client keeps a connection open to a server, waiting for data to become available. This reduces the need for frequent requests.

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What is short polling?

In contrast to long polling, short polling involves a client sending requests to the server at regular intervals to check for updates.

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What is rendering in web development?

Rendering is the process of converting digital data into a visual representation, typically displayed on a screen.

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What is the process of fetching data from a server?

The process of fetching data from a server, processing it, and then displaying it on the user's screen.

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readystate (XMLHttpRequest)

The state of the XMLHttpRequest object, indicating its interaction with the server.

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XMLHttpRequest

An object in JavaScript that allows web pages to send and receive data from a server without reloading the page.

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onreadystatechange

A method attached to the XMLHttpRequest object that defines a function to automatically execute whenever the readyState changes.

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Status code (XMLHttpRequest)

The code returned by the server as a response to the request, e.g. 200 indicates success, 404 indicates a file not found.

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responseText (XMLHttpRequest)

The textual data returned by the server in response to the request. It contains the actual content of the response.

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AJAX

A set of web development techniques using JavaScript and XMLHttpRequest for dynamic content updates without full page reloads.

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Asynchronous JavaScript

The ability for JavaScript to run without waiting for the server's response. The server's response will be processed once it arrives.

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AJAX for Suggesting Values

Utilizing AJAX to dynamically update portions of a webpage, such as an autocomplete feature that suggests values as a user types.

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XMLHttpRequest open() method

A method that establishes a connection between the browser and the server, specifying the communication type (GET or POST) and the target URL.

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XMLHttpRequest send() method

A method that sends an HTTP request to the server, including any data to be sent.

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HTTP Method in open() method

The type of HTTP request to be sent to the server. It can either be GET, POST, PUT, DELETE, etc.

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URL in open() method

The URL of the server-side script or resource that will handle the request.

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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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HTTP and AJAX for Web Development PDF

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