AJAX Overview and HTTP Protocol

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Questions and Answers

What does the readyState property of XMLHttpRequest indicate?

  • The type of the HTTP request
  • The current state of the XMLHttpRequest object (correct)
  • The number of bytes received
  • The server's response time

What readyState value indicates that the object has been created but not yet initialized?

  • 1
  • 2
  • 0 (correct)
  • 3

Which status code indicates a successful request in XMLHttpRequest?

  • 200 (correct)
  • 404
  • 500
  • 302

Which method property is used to handle changes in the readyState of XMLHttpRequest?

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

At which readyState is the response currently being processed?

<p>3 (A)</p> Signup and view all the answers

What does HTTP stand for?

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

What happens when a request is sent to the server?

<p>A new connection is established for each request. (D)</p> Signup and view all the answers

How does HTTP handle state between requests?

<p>It is a stateless protocol. (C)</p> Signup and view all the answers

What is the drawback of short polling?

<p>It does not allow for data updates to be pushed. (C)</p> Signup and view all the answers

What is one characteristic of long polling?

<p>The server pushes updates as they become available. (D)</p> Signup and view all the answers

What happens after the client receives data from a long polling request?

<p>The client must send a new request to continue receiving updates. (A)</p> Signup and view all the answers

Which statement accurately describes HTTP's nature?

<p>It functions independently of previous requests. (B)</p> Signup and view all the answers

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

<p>By minimizing the number of unnecessary requests. (C)</p> Signup and view all the answers

What is the primary purpose of rendering in web development?

<p>To generate HTML markup for web page display. (A)</p> Signup and view all the answers

Which of the following is true about XMLHttpRequest?

<p>It allows fetching data in various formats, including JSON and HTML. (A)</p> Signup and view all the answers

What does the term 'asynchronous' mean in the context of AJAX?

<p>JavaScript execution continues while waiting for the response. (C)</p> Signup and view all the answers

Which method would you use to establish a connection in XMLHttpRequest?

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

What must be changed if using POST method in XMLHttpRequest?

<p>The type MIME of the request must be defined. (D)</p> Signup and view all the answers

What does the 'open' method's 'aAsync' parameter define?

<p>Whether the request is asynchronous or synchronous. (B)</p> Signup and view all the answers

In which scenario would you use the GET method with XMLHttpRequest?

<p>When the data can be included in the URL as parameters. (A)</p> Signup and view all the answers

What is a key benefit of using AJAX in web applications?

<p>It allows partial page updates without full reloads. (C)</p> Signup and view all the answers

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Flashcards

What is HTTP?

HTTP is a protocol that allows web browsers and servers to communicate and exchange information.

How does HTTP work?

Clients, like web browsers, send requests to servers and the servers respond with data. It's a request-response cycle.

Why is HTTP stateless?

After processing a request, the server closes the connection. Every new request requires a new connection to be established.

What is long polling?

Long polling keeps the connection between the server and client 'open' until there's new data available. It's more efficient than constantly sending requests.

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What is short polling?

Short polling is a less efficient approach where the client repeatedly sends requests, even when there's no new information.

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What is rendering?

Rendering is the process of taking code and data, and transforming it into a visual representation you see on your screen.

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How does long polling improve efficiency?

Long polling is more efficient than traditional short polling because it reduces the number of requests needed to get new information.

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When is long polling useful?

Long polling is often used in applications where real-time updates are necessary, such as chat applications, live dashboards, and social media notifications.

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AJAX

A set of established techniques primarily relying on XMLHttpRequest, a client-side JavaScript object. It's used to fetch data in various formats—XML, JSON, HTML, or simple text—using HTTP requests.

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XMLHttpRequest

A JavaScript object that enables retrieving data from a server in formats such as XML, JSON, HTML, or plain text through HTTP requests.

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Dynamic Page Update with AJAX

A technique that allows for partial updates of web pages without reloading the entire page, improving user experience by updating content dynamically.

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Asynchronous Execution in AJAX

It means that the code execution continues without waiting for the server's response. The response is processed upon arrival.

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open() method in AJAX

A method used to establish a connection with a server. It takes the HTTP method, URL, and asynchronicity as arguments.

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send() method in AJAX

A method used to send a request to the server. It also defines the data to be sent for POST requests and requires setting the request header type.

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HTTP Method in AJAX

The type of request used in AJAX, determines how the data is sent to the server. Methods like GET are used to retrieve data, while POST sends data to the server.

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URL in AJAX

It indicates the URL of the server-side script responsible for processing the AJAX request. It can be a dynamic (PHP, ASP) or static (TXT, HTML) file.

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XMLHttpRequest readyState

A property of the XMLHttpRequest object representing the current state of the request. It indicates whether the request has been initiated, connected, sent, receiving data, or completed.

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XMLHttpRequest onreadystatechange

A method of the XMLHttpRequest object that defines a function to be executed whenever the readyState changes.

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XMLHttpRequest response

A property of the XMLHttpRequest object that provides the status code returned by the server. Common codes include 200 for success and 404 for 'not found.'

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XMLHttpRequest responseText

A property of the XMLHttpRequest object holding the text-based response from the server.

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XMLHttpRequest responseXML

A property of the XMLHttpRequest object containing the response from the server in XML format.

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Study Notes

AJAX Overview

  • AJAX stands for Asynchronous JavaScript and XML
  • It's a set of techniques used to update parts of a web page without reloading the entire page
  • This improves user experience

HTTP Protocol

  • HTTP stands for Hypertext Transfer Protocol
  • It's an application layer protocol used for transferring data across the web
  • HTTP enables clients (e.g., web browsers) and servers to share information
  • HTTP protocol operates on a client-server model
  • When a request is sent to the server, a connection is established
  • The server processes the request and sends back a response
  • The connection is closed when the response is sent
  • If another request is sent, it's treated as a new request
  • This triggers a new connection for the new request to be processed
  • HTTP is a stateless protocol; the server forgets everything about the client/browser state
  • Each request is independent of the others

Long Polling

  • Traditional web browsers use a pull-based approach (short polling) to fetch data.
  • This approach increases the network overhead as the client repeatedly sends requests to check for updates
  • The server processes unnecessary requests, even if there's no new data
  • Long polling is a push-based approach
  • It allows the server to send updates to the client as soon as they become available
  • Maintains the HTTP connection to allow the server to reply later when data is available or the timeout threshold has been reached
  • The client only needs to send one request to fetch the latest information
  • The client can initiate a new request after receiving the data, repeating this process as necessary.

Rendering

  • Rendering is the process of generating HTML markup to display web pages
  • How and where the rendering process happens affects user experience, site performance, and SEO
  • This is a critical consideration in web page design and development

AJAX Functionality

  • AJAX is built on existing techniques, primarily leveraging XMLHttpRequest- a client-side Javascript object
  • XMLHttpRequest allows fetching data (XML, JSON, HTML, or plain text) from a server using HTTP requests.
  • AJAX enables partial page updates, without full page reloads.
  • The asynchronicity of AJAX means Javascript continues its execution without waiting for a server response.
  • The server's response is processed later

AJAX Example Usage

  • AJAX can be used to provide suggestions and autocomplete functionality
  • Google is a prominent example of AJAX use

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HTTP and AJAX for Web Development PDF

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