Podcast
Questions and Answers
What is the primary responsibility of the interface construction in traditional web applications?
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?
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?
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?
Which of the following indicates a traditional web application model?
Which method can be used to identify an Ajax application when inspecting the source?
Which method can be used to identify an Ajax application when inspecting the source?
What happens to the application during user interactions in an Ajax environment?
What happens to the application during user interactions in an Ajax environment?
Which of the following is NOT a feature of Ajax web applications?
Which of the following is NOT a feature of Ajax web applications?
What is a significant drawback of the classic web application model?
What is a significant drawback of the classic web application model?
What does the acronym Ajax stand for?
What does the acronym Ajax stand for?
Which component is primarily responsible for asynchronous data retrieval in Ajax?
Which component is primarily responsible for asynchronous data retrieval in Ajax?
Which technology did Microsoft first implement to enable Ajax in Internet Explorer?
Which technology did Microsoft first implement to enable Ajax in Internet Explorer?
Which feature is not characteristic of Ajax applications?
Which feature is not characteristic of Ajax applications?
What was the main function of the server in an Ajax-enabled application?
What was the main function of the server in an Ajax-enabled application?
Which of the following technologies is NOT traditionally associated with Ajax?
Which of the following technologies is NOT traditionally associated with Ajax?
Who originated the acronym Ajax?
Who originated the acronym Ajax?
Which standard encompasses similar functionality to the XMLHttpRequest object?
Which standard encompasses similar functionality to the XMLHttpRequest object?
What is one primary benefit of using Ajax in web applications?
What is one primary benefit of using Ajax in web applications?
Which operation can the Ajax engine handle on its own without server interaction?
Which operation can the Ajax engine handle on its own without server interaction?
What is a key feature of the Ajax model compared to traditional web application models?
What is a key feature of the Ajax model compared to traditional web application models?
What does the Ajax engine implement to initiate user actions?
What does the Ajax engine implement to initiate user actions?
How does the Ajax engine improve application responsiveness for users?
How does the Ajax engine improve application responsiveness for users?
What needs to be created to handle asynchronous requests in Ajax?
What needs to be created to handle asynchronous requests in Ajax?
What is a disadvantage of traditional web application models compared to Ajax?
What is a disadvantage of traditional web application models compared to Ajax?
What form of data can the Ajax engine retrieve from the server?
What form of data can the Ajax engine retrieve from the server?
What are the two required parameters for the open() method?
What are the two required parameters for the open() method?
What is the primary purpose of the send() method in the XMLHttpRequest object?
What is the primary purpose of the send() method in the XMLHttpRequest object?
Which readyState value indicates that the transaction is complete?
Which readyState value indicates that the transaction is complete?
In what scenario should the POST method be used with the XMLHttpRequest object?
In what scenario should the POST method be used with the XMLHttpRequest object?
What type of data does the responseText property return?
What type of data does the responseText property return?
Which method should typically be designed around the onreadystatechange event?
Which method should typically be designed around the onreadystatechange event?
What is a key characteristic of the responseXML property of the XMLHttpRequest object?
What is a key characteristic of the responseXML property of the XMLHttpRequest object?
Why is it considered safer to send requests asynchronously in XMLHttpRequest?
Why is it considered safer to send requests asynchronously in XMLHttpRequest?
What are the possible values for the responseType attribute of the XMLHttpRequest object?
What are the possible values for the responseType attribute of the XMLHttpRequest object?
In the onreadystatechange function, under what condition is the response processed?
In the onreadystatechange function, under what condition is the response processed?
Which method is used to alert the user about a problem with the XMLHttpRequest?
Which method is used to alert the user about a problem with the XMLHttpRequest?
What must the protocol be for the page accessing the XMLHttpRequest object?
What must the protocol be for the page accessing the XMLHttpRequest object?
What security policy does the XMLHttpRequest comply with while running in a browser?
What security policy does the XMLHttpRequest comply with while running in a browser?
What happens if a script tries to access a resource from a different domain using XMLHttpRequest?
What happens if a script tries to access a resource from a different domain using XMLHttpRequest?
What does req.responseText return when the responseType is set to json?
What does req.responseText return when the responseType is set to json?
Which browsers are specifically mentioned as having potential issues with testing XMLHttpRequest from a local hard disk?
Which browsers are specifically mentioned as having potential issues with testing XMLHttpRequest from a local hard disk?
What type of data can be accessed from any domain without security risk?
What type of data can be accessed from any domain without security risk?
What is one of the ways mentioned to circumvent cross-domain security restrictions?
What is one of the ways mentioned to circumvent cross-domain security restrictions?
What must a server be configured to accept if using CORS?
What must a server be configured to accept if using CORS?
Why is it not possible for a web application to directly access data from a different domain?
Why is it not possible for a web application to directly access data from a different domain?
Which of the following accurately describes the Fetch API?
Which of the following accurately describes the Fetch API?
What is one drawback of using a proxy for cross-domain requests?
What is one drawback of using a proxy for cross-domain requests?
Which function does the Fetch API provide for making network requests?
Which function does the Fetch API provide for making network requests?
What is the purpose of CORS in web applications?
What is the purpose of CORS in web applications?
Flashcards
Ajax
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
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)
XMLHttpRequest (XHR)
A JavaScript object used for asynchronous communication with a web server, part of Ajax technology.
JSON
JSON
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DOM Manipulation
DOM Manipulation
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Full-Page Refresh
Full-Page Refresh
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Asynchronous Communication
Asynchronous Communication
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Web Mashups
Web Mashups
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Traditional Web Application
Traditional Web Application
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Ajax Web Application
Ajax Web Application
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Interface Construction (Ajax)
Interface Construction (Ajax)
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Document Object Model (DOM)
Document Object Model (DOM)
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XMLHttpRequest
XMLHttpRequest
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HTTP Request
HTTP Request
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Application Speed (Ajax)
Application Speed (Ajax)
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Ajax Engine
Ajax Engine
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Asynchronous Interaction
Asynchronous Interaction
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XMLHttpRequest Object
XMLHttpRequest Object
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JSON/XML
JSON/XML
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JavaScript Call
JavaScript Call
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Ajax Engine Role (Simple)
Ajax Engine Role (Simple)
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Ajax Engine Role (Complex)
Ajax Engine Role (Complex)
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XMLHttpRequest Object Methods
XMLHttpRequest Object Methods
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XMLHttpRequest open()
method
XMLHttpRequest open()
method
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XMLHttpRequest send()
method
XMLHttpRequest send()
method
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HTTP method 'GET'
HTTP method 'GET'
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HTTP method 'POST'
HTTP method 'POST'
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XMLHttpRequest readyState
property
XMLHttpRequest readyState
property
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XMLHttpRequest responseText
property
XMLHttpRequest responseText
property
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XMLHttpRequest responseXML
property
XMLHttpRequest responseXML
property
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XMLHttpRequest responseType
XMLHttpRequest responseType
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responseType options
responseType options
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XMLHttpRequest response property
XMLHttpRequest response property
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req.readyState
req.readyState
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req.status
req.status
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Same-origin policy
Same-origin policy
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HTTP protocol
HTTP protocol
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Local file access
Local file access
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Cross-domain Security
Cross-domain Security
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Image Exception
Image Exception
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Proxy solution
Proxy solution
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Fetch API
Fetch API
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CORS (Cross-Origin Resource Sharing)
CORS (Cross-Origin Resource Sharing)
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Why a Proxy is Needed
Why a Proxy is Needed
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Web Applications and Yahoo!
Web Applications and Yahoo!
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Request Relay
Request Relay
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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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