XMLHttpRequest and Browser Support
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Questions and Answers

Which browser was the first to implement a native version of XMLHttpRequest?

  • Mozilla 1.0 (correct)
  • Opera 7.6
  • Safari 1.2
  • Firefox 1.0

    • What is the name of the W3C standard that covers similar functionality to XMLHttpRequest?

  • XMLHttpRequest Living Standard
  • DOM Level 2 Load and Save Specification
  • DOM Level 3 Load and Save Specification (correct)
  • Ajax Standard Specification

    • In which year was XMLHttpRequest moved to the WHATWG?

  • 2006
  • 2004
  • 2012 (correct)
  • 2007

    • What is the characteristic of Google Maps that is demonstrated in the example?

    <p>The page is never explicitly refreshed</p> Signup and view all the answers

    Where can the XMLHttpRequest specification be found online?

    <p><a href="https://xhr.spec.whatwg.org/">https://xhr.spec.whatwg.org/</a></p> Signup and view all the answers

    What is the value that signals the completion of the transaction?

    <p>4</p> Signup and view all the answers

    What type of document is returned by the responseXML property?

    <p>XML document</p> Signup and view all the answers

    What is the primary method used to get JSON data in today's implementations?

    <p>responseText property</p> Signup and view all the answers

    What is the purpose of the responseType attribute in the XMLHttpRequest Living Standard?

    <p>To specify the type of response expected from the server</p> Signup and view all the answers

    What is returned by the response property when json is selected in the XMLHttpRequest Living Standard?

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

    What is the optional parameter that can be passed to the fetch() method?

    <p>An init object</p> Signup and view all the answers

    What is the purpose of the initAll function in the provided JavaScript code?

    <p>To set up event listeners for button clicks</p> Signup and view all the answers

    What is the condition for the xhr object to be created as an ActiveXObject?

    <p>If the browser does not support XMLHttpRequest</p> Signup and view all the answers

    What is the purpose of the showContents function in the provided JavaScript code?

    <p>To display the response from the server in the browser</p> Signup and view all the answers

    What is the method used to send the request in the provided JavaScript code?

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

    What is the property of the xhr object that is checked to determine if the request has completed successfully?

    <p>xhr.readyState</p> Signup and view all the answers

    What is the purpose of the initAll function in the second Ajax script?

    <p>To create a new XMLHttpRequest object</p> Signup and view all the answers

    What is the method used to send the request to the server in the second Ajax script?

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

    What is the purpose of the tempDiv variable in the showPictures function?

    <p>To create a new DOM element to hold the response text</p> Signup and view all the answers

    What is the condition for the xhr.readyState property in the showPictures function?

    <p>xhr.readyState == 4</p> Signup and view all the answers

    What is the purpose of the pageDiv variable in the showPictures function?

    <p>To get a reference to the existing DOM element with the id 'pictureBar'</p> Signup and view all the answers

    What is the file type of the file being retrieved from Flickr in the second Ajax script?

    <p>XML file</p> Signup and view all the answers

    What is an alternative to using a proxy to make requests to Yahoo!?

    <p>CORS</p> Signup and view all the answers

    What is the primary benefit of using a proxy to relay requests to Yahoo!?

    <p>To bypass same-origin policy restrictions</p> Signup and view all the answers

    What is a key difference between the Fetch API and jQuery.ajax()?

    <p>Fetch API won't reject on HTTP error status, while jQuery.ajax() will</p> Signup and view all the answers

    What is required to use CORS?

    <p>A server that is set up to accept CORS requests</p> Signup and view all the answers

    What does the Fetch API provide a single logical place for defining?

    <p>HTTP-related concepts such as CORS and HTTP extensions</p> Signup and view all the answers

    What is silently ignored by the Fetch API?

    <p>Set-Cookie headers from other sites</p> Signup and view all the answers

    Study Notes

    • XMLHttpRequest is a compatible native version implemented by Mozilla project for Mozilla 1.0 and later releases, including Netscape 7 and Firefox 1.0.

    • Apple also implemented XMLHttpRequest starting with Safari 1.2, and other browsers supporting it include Opera 7.6+ and all mobile browsers.

    • XMLHttpRequest was moved to W3C in 2006 and back to WHATWG in 2012 as XMLHttpRequest Living Standard, with a specification available at https://xhr.spec.whatwg.org/.

    • Google Maps uses XMLHttpRequest, as evident from the page's source code, which does not explicitly refresh the page.

    • One way to work around the issue of using XMLHttpRequest to request data from another domain is to install a web proxy on the server that passes requests from the application to the target domain and sends the data back.

    • Another way to work around this issue is to use CORS (Cross-Origin Resource Sharing), which works on all recent browsers, but requires a server that is set up to accept CORS requests.

    • The Fetch API provides a JavaScript interface for accessing and manipulating requests and responses, and also provides a global fetch() method to fetch resources asynchronously.

    • The Fetch API differs from jQuery.ajax() in three main ways: it won't reject on HTTP error status, it won't receive cross-site cookies, and it won't send cookies unless the credentials init option is set.

    • The XMLHttpRequest object has a responseType attribute that can be set to arraybuffer, blob, document, json, and text, and a response property that returns a parsed JSON object when json is selected.

    • The fetch() method can optionally accept a second parameter, an init object that allows controlling a few settings.

    • A simple Ajax example uses a JavaScript file to request a text file and an XML file, and display the returned data in the browser.

    • The XMLHttpRequest object has an onreadystatechange event handler that is called when the readyState changes, and the readyState property has a value of 4 when the request is complete.

    • The status property of the XMLHttpRequest object returns the HTTP status code of the response, and the responseText property returns the response data as a string.

    • The responseXML property returns the response data as an XML document object, which can be examined and parsed using W3C DOM node tree methods and properties.

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    Description

    This quiz covers the history and implementation of XMLHttpRequest in different browsers, including Mozilla, Apple Safari, and Opera. Learn about the W3C standard and how it was adopted by various browsers.

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