Ajax vs Traditional Web Applications

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Questions and Answers

What is the primary responsibility of the interface construction in traditional web applications?

  • Manipulation of the Document Object Model (DOM)
  • Background HTTP requests
  • Server processing (correct)
  • Client-side JavaScript manipulations

How does user interaction occur in Ajax applications compared to traditional applications?

  • Directly via the server responses
  • Only through page refresh
  • Via form submissions only
  • Through HTTP requests that occur ‘behind the scenes’ (correct)

What does the Ajax engine primarily do during a user session?

  • Handles all traditional form submissions
  • Pre-loads data into the browser cache
  • Renders the interface and communicates with the server (correct)
  • Loads all HTML pages directly from the server

Which of the following indicates a traditional web application model?

<p>User waits for the server to process requests (A)</p> Signup and view all the answers

Which method can be used to identify an Ajax application when inspecting the source?

<p>Finding XMLHttpRequest or fetch invocations (B)</p> Signup and view all the answers

What happens to the application during user interactions in an Ajax environment?

<p>Only data is communicated, keeping the interface responsive (D)</p> Signup and view all the answers

Which of the following is NOT a feature of Ajax web applications?

<p>Triggering HTTP requests to load entire web pages (B)</p> Signup and view all the answers

What is a significant drawback of the classic web application model?

<p>Users experience delays with every action (D)</p> Signup and view all the answers

What does the acronym Ajax stand for?

<p>Asynchronous JavaScript and XML (C)</p> Signup and view all the answers

Which component is primarily responsible for asynchronous data retrieval in Ajax?

<p>XMLHttpRequest (C)</p> Signup and view all the answers

Which technology did Microsoft first implement to enable Ajax in Internet Explorer?

<p>ActiveX Object (C)</p> Signup and view all the answers

Which feature is not characteristic of Ajax applications?

<p>Full-Page Refresh (A)</p> Signup and view all the answers

What was the main function of the server in an Ajax-enabled application?

<p>Business Logic Processing (C)</p> Signup and view all the answers

Which of the following technologies is NOT traditionally associated with Ajax?

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

Who originated the acronym Ajax?

<p>Jesse James Garrett (D)</p> Signup and view all the answers

Which standard encompasses similar functionality to the XMLHttpRequest object?

<p>W3C DOM Level 3 Load and Save Specification (B)</p> Signup and view all the answers

What is one primary benefit of using Ajax in web applications?

<p>It cuts down on user wait time. (D)</p> Signup and view all the answers

Which operation can the Ajax engine handle on its own without server interaction?

<p>Editing data in memory. (D)</p> Signup and view all the answers

What is a key feature of the Ajax model compared to traditional web application models?

<p>Operates asynchronously. (A)</p> Signup and view all the answers

What does the Ajax engine implement to initiate user actions?

<p>JavaScript calls. (A)</p> Signup and view all the answers

How does the Ajax engine improve application responsiveness for users?

<p>By allowing background data retrieval without halting user interaction. (B)</p> Signup and view all the answers

What needs to be created to handle asynchronous requests in Ajax?

<p>An instance of the XMLHttpRequest object. (A)</p> Signup and view all the answers

What is a disadvantage of traditional web application models compared to Ajax?

<p>Users see frequent hourglass cursors. (D)</p> Signup and view all the answers

What form of data can the Ajax engine retrieve from the server?

<p>JSON or XML data. (D)</p> Signup and view all the answers

What are the two required parameters for the open() method?

<p>HTTP method and URL (B)</p> Signup and view all the answers

What is the primary purpose of the send() method in the XMLHttpRequest object?

<p>To initiate the transaction (C)</p> Signup and view all the answers

Which readyState value indicates that the transaction is complete?

<p>4 (B)</p> Signup and view all the answers

In what scenario should the POST method be used with the XMLHttpRequest object?

<p>When sending large amounts of data to the server (C)</p> Signup and view all the answers

What type of data does the responseText property return?

<p>A string representation of data (B)</p> Signup and view all the answers

Which method should typically be designed around the onreadystatechange event?

<p>send() (C)</p> Signup and view all the answers

What is a key characteristic of the responseXML property of the XMLHttpRequest object?

<p>It is a full XML document node object (A)</p> Signup and view all the answers

Why is it considered safer to send requests asynchronously in XMLHttpRequest?

<p>It allows multiple requests to be processed concurrently (D)</p> Signup and view all the answers

What are the possible values for the responseType attribute of the XMLHttpRequest object?

<p>arraybuffer, blob, document, json, text (B)</p> Signup and view all the answers

In the onreadystatechange function, under what condition is the response processed?

<p>When req.readyState is 4 and req.status is 200 (B)</p> Signup and view all the answers

Which method is used to alert the user about a problem with the XMLHttpRequest?

<p>alert() (B)</p> Signup and view all the answers

What must the protocol be for the page accessing the XMLHttpRequest object?

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

What security policy does the XMLHttpRequest comply with while running in a browser?

<p>Same-origin policy (A)</p> Signup and view all the answers

What happens if a script tries to access a resource from a different domain using XMLHttpRequest?

<p>The request will fail due to security restrictions. (D)</p> Signup and view all the answers

What does req.responseText return when the responseType is set to json?

<p>A parsed JSON object (A)</p> Signup and view all the answers

Which browsers are specifically mentioned as having potential issues with testing XMLHttpRequest from a local hard disk?

<p>Mozilla and Internet Explorer (C)</p> Signup and view all the answers

What type of data can be accessed from any domain without security risk?

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

What is one of the ways mentioned to circumvent cross-domain security restrictions?

<p>Setting up a web proxy (B)</p> Signup and view all the answers

What must a server be configured to accept if using CORS?

<p>CORS requests (C)</p> Signup and view all the answers

Why is it not possible for a web application to directly access data from a different domain?

<p>It violates the browser's cross-domain security policy. (B)</p> Signup and view all the answers

Which of the following accurately describes the Fetch API?

<p>A JavaScript interface for accessing and manipulating requests and responses. (B)</p> Signup and view all the answers

What is one drawback of using a proxy for cross-domain requests?

<p>It requires additional server-side configuration. (C)</p> Signup and view all the answers

Which function does the Fetch API provide for making network requests?

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

What is the purpose of CORS in web applications?

<p>To allow secure cross-origin requests. (C)</p> Signup and view all the answers

Flashcards

Ajax

A set of technologies used for web development that allows for asynchronous communication between the web browser and server, avoiding full page refreshes.

Asynchronous JavaScript + XML

Describes a set of technologies within Ajax that enables dynamic web applications with efficient communication between web browser and server.

XMLHttpRequest (XHR)

A JavaScript object used for asynchronous communication with a web server, part of Ajax technology.

JSON

A lightweight data-interchange format used in Ajax, primarily for exchanging data between web browsers and servers.

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DOM Manipulation

Dynamic changes of web page content, elements, and structure using JavaScript. Modifying the content of a webpage without reloading

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Full-Page Refresh

Outdated web page loading method. The entire web page is reloaded from the server when content changes.

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Asynchronous Communication

A method of communication where two or more units or systems can work together without waiting for a single response. The web browser communicates with a server and receives data without waiting for the full content.

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Web Mashups

Web pages that combine data from multiple sources in one location. Think about putting content from different websites together on to one page.

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Traditional Web Application

A web application where the server is primarily responsible for constructing the interface, and user interactions trigger complete page reloads.

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Ajax Web Application

A web application that uses JavaScript to dynamically update parts of a webpage without requiring a full page reload. Communication with the server happens in the background using HTTP requests.

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Interface Construction (Ajax)

The part of a web page that a user sees and interacts with. Using AJAX, the front end is developed by JavaScript, not the server, unlike traditional web applications.

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Document Object Model (DOM)

A programming interface for HTML and XML documents. It represents the structure of a document as a tree of objects, allowing JavaScript to access and modify individual elements.

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XMLHttpRequest

A browser API that allows JavaScript to make asynchronous HTTP requests to a server without interfering with the rest of the page.

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HTTP Request

A communication protocol in the web that AJAX uses to submit information to the server without reloading the whole page.

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Application Speed (Ajax)

The ability of an AJAX web application to remain responsive while the Ajax engine communicates with the server and updates content in the background.

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Ajax Engine

An intermediary JavaScript program that handles communication with the server on behalf of the user to update a web page.

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Asynchronous Interaction

User interaction that happens independently of communication with the server, allowing the application to stay responsive.

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XMLHttpRequest Object

Object used to manage asynchronous communication with the server in Ajax applications.

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JSON/XML

Formats used to exchange data between the client and server in an Ajax application.

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JavaScript Call

A way of initiating communication for user actions in Ajax; instead of an HTTP request, a JavaScript call is used to interact with the application.

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Ajax Engine Role (Simple)

Handles user actions to communicate without page reloads.

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Ajax Engine Role (Complex)

A JavaScript component that handles web application interactions and manages requests to the server asynchronously. It handles simple actions locally and makes requests to the server when needed, such as submitting, loading, or retrieving new information.

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XMLHttpRequest Object Methods

Functions that control operations and handle data, with open() and send() used most often.

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XMLHttpRequest open() method

Prepares an operation by setting the HTTP request method and URL.

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XMLHttpRequest send() method

Starts the HTTP operation.

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HTTP method 'GET'

Used for retrieving data from the server.

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HTTP method 'POST'

Used for sending data to the server.

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XMLHttpRequest readyState property

Shows the current status of an HTTP request.

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XMLHttpRequest responseText property

Contains the response from the server as a string, often used with JSON.

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XMLHttpRequest responseXML property

Contains the response from the server as an XML document.

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XMLHttpRequest responseType

A property used to specify the type of data expected from a server-side response.

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responseType options

Options like 'arraybuffer', 'blob', 'document', 'json', and 'text' to define how the response will be formatted.

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XMLHttpRequest response property

When responseType is 'json', returns a parsed JSON object; otherwise, returns the response as a string or other format according to responseType.

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req.readyState

A property of 'req' that indicates the state of the XMLHttpRequest request (e.g., uninitialized, loading, ready, done).

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req.status

Status code from server response (e.g., 200 for success, 404 not found).

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Same-origin policy

Security restriction that prevents a script from accessing resources from a different domain.

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HTTP protocol

Standard used for communication between web browsers and servers.

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Local file access

Accessing files from a computer's local storage.

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Cross-domain Security

A browser security restriction that prevents scripts from accessing data from a different domain than the one they originate from.

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Image Exception

Images are exempt from cross-domain security restrictions, allowing them to be displayed from any domain.

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Proxy solution

A server that acts as an intermediary, forwarding requests from one domain to another, bypassing cross-domain restrictions.

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Fetch API

A JavaScript interface for making network requests, providing a modern way to handle requests and responses compared to older methods.

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CORS (Cross-Origin Resource Sharing)

A mechanism that allows servers to define which domains can access their resources, providing a way to control cross-domain access.

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Why a Proxy is Needed

A proxy server is essential for cross-domain communication because it acts as a middleman, allowing your application to communicate with other domains.

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Web Applications and Yahoo!

A web application wants to use data from both its own site and Yahoo! but this is restricted due to cross-domain security policies.

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Request Relay

In a proxy setup, the actual request URL used by your application is different because it needs to go through the proxy server.

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Study Notes

Ajax - Asynchronous JavaScript + XML

  • Ajax is not a single technology but rather a combination of several technologies
  • It incorporates standards-based presentation using XHTML, CSS, and dynamic display/interaction via the Document Object Model (DOM)
  • Data interchange can use XML, but JSON is more common today
  • Asynchronous data retrieval uses XMLHttpRequest
  • JavaScript binds all these elements together
  • Server-side logic is focused on business logic, not display logic

Ajax Application Characteristics

  • Ajax applications are interactive, rather than just static web pages
  • User interaction is continuous and smooth
  • Data is loaded asynchronously without requiring page refresh
  • Animations and dynamic icons enhance user engagement
  • New widgets, such as dropdown menus, tabs, and lists are added
  • New styles of interaction, like drag-and-drop and keyboard shortcuts are used

Comparing Traditional vs. AJAX Websites

Feature Traditional AJAX
Interface Constructed primarily by the server Manipulated by client-side JavaScript
User Interaction Form submissions HTTP requests (behind the scenes)
Page Refresh An entire page is loaded per interaction Updates are made without full page refresh
Application State Application unavailable while processing Responsive during processing

How to Recognize an Ajax Application Internally

  • Examine the Javascript source code for XMLHttpRequest or fetch calls
  • Look for JavaScript loading other JavaScript files
  • Look for code passed as text strings to the server
  • Examine Javascript code between //
  • Search for Javascript code creating IFRAMEs or including jQuery Ajax functions.

The Classic vs. Ajax Web Application Model

  • Classic Model: User actions trigger HTTP requests to the server, which then sends back an HTML page. User waits for each step.
  • Ajax Model: An intermediary (Ajax engine) handles requests and updates, allowing interactions to happen asynchronously. No waiting for full page reloads.

AJAX: Client-Side Processing

  • AJAX significantly reduces the time the user has to wait for server actions.
  • Reduces the amount of network traffic that the application sends to the web server and then back to the browser.
  • Client-side processing enhances interactivity and responsiveness of applications.

Security Issues with AJAX

  • AJAX inherits security policies of typical JavaScript
  • For cross-domain interactions, the URL must be from the same domain as the page that contains the script.
  • Using a proxy or CORS configurations often help mitigate cross-domain issues.

Cross-Origin Resource Sharing (CORS)

  • CORS is a mechanism that enables a web application to make requests to other domains.
  • The server explicitly permits such requests through HTTP headers (like Access-Control-Allow-Origin)
  • Browsers use this information to decide whether to allow access.

Alternative: Fetch API

  • Fetch API is a more modern way to fetch resources asynchronously with improved error handling and global methods.
  • Promises returned from fetch won't reject on HTTP errors, even if the returned status code is not 200.
  • It doesn't automatically receive cookies from other domains unless credentials are set.
  • Main characteristics differ from jQuery. AJAX in three ways: Promises, HTTP errors, cross-domain cookies

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