• The Application-Layer Protocol:
  • Hypertext Transfer Protocol
• The Important Classes:
  • XMLHttpRequest
  • XMLDOM
• The Process:
  • Create an XMLHttpRequest object
  • Call the open() method
  • Call the send() method
  • Either synchronously or asynchronoulsy, wait for the response
  • Construct an XMLDOM object from the response
  • Work with the XMLDOM object

• Parameters of the open() Method:
  • The request type ("GET" or "POST")
  • The URL
  • false for synchronous, true for asynchronous
• Parameters of the send() Method:
  • The optional parameter can be used to include ampersand-delimited name=value lines in a POST request
• Another Useful Method:
  • The setRequestHeader(header,value) method can be used to add HTTP headers to the request

• After the Call Returns:
  • The XMLHttpRequest object will contain the response
• Accessing the Response:
  • An XML response will be in the responseXML attribute
  • A text response will be in the responseText attribute
• For Asynchronous Requests:
  • The XMLHttpRequest object's onreadstatechange attribute must contain the function to call

A Weight Retriever

ecmascriptexamples/http/alice.xml ecmascriptexamples/http/weight-retriever.html ecmascriptexamples/http/weight-retriever.js

• Purpose:
  • A generic slideshow "web app" that retrieves the slides
• Some Obervations:
  • An XML file contains the slides
  • The easiest way to structure the slides is to use HTML
• The Implication:
  • To make sure the HTML in the HTML file isn't parsed, we need to make it "data"

A Slideshow App

ecmascriptexamples/http/slideshow.html ecmascriptexamples/http/slideshow.css ecmascriptexamples/http/slides.xml ecmascriptexamples/http/SlidePresenter.js ecmascriptexamples/http/slideshow.js

• Suppose:
  • You want to include the name of the file containing the slides in the query string of the URL
• Getting the URL:
  • document.URL (part of the DOM)
  • window.location (non-standard but supported)
• Working with the URL:
  • The global decodeURI() and encodeURI() functions can be used to convert from/to the standard encoding (e.g., no spaces)
  • Strings have lastIndexOf() and split() methods that can be used to tokenize the URL