Beginning JavaScript with DOM Scripting and Ajax, 2nd Edition

CHAPTer 8 ■ BACk-end InTerACTIon wITH AjAx And node.js
■ Note These links are not totally unobtrusive and up to the standard of the rest of the code examples in this book,
but at least they work without javascript—the browser will simply show the text files when scripting is not available.
It is very tempting, especially when using out-of-the-box Ajax libraries, to create scripting-dependent links. no matter
how cool the technology is, this is never a good idea.
simpleXHR.js
simplexhr = {
doxhr : function( container, url ) {
if( !document.getElementById || !document.createTextNode) {
return;
}
simplexhr.outputContainer = document.getElementById( container );
if( !simplexhr.outputContainer ){ return; }
The script starts by checking for the DOM and checking whether the element you want to write content into is
available. If the element is available, it gets stored in a property called outputContainer to make it available for all
other methods in the script.
simpleXHR.js (continued)
var request;
try{
request = new XMLHttpRequest();
} catch ( error ) {
try {
request = new ActiveXObject("Microsoft.XMLHTTP" );
} catch ( error ) {
return true;
}
}
Define a new variable called request and use the try and catch construct to see which XHR version is supported.
Try assigning a new XMLHttpRequest. If that is not supported, an error occurs that triggers the catch statement. (You
can learn more about try and catch() in the appendix of this book.) This one tries to assign the Microsoft ActiveX
object instead. If that is not available either, the method returns true, which means the browser will just follow the
link and show the text in the browser.
If the assignment was successful, you have a new XMLHttpRequest object at your disposal.
■ Note For a complete list of methods, handlers, and properties of the XMLHttpRequest object, you can consult the
documentation at the w3C site: http://www.w3.org/TR/XMLHttpRequest/. You can also refer to the Mozilla developer
network at https://developer.mozilla.org/en-US/docs/DOM/XMLHttprequest or the Microsoft web site at
http://msdn.microsoft.com/en-us/library/ms535874%28v=vs.85%29.aspx.
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