Accessing webservices via Javascript (aka AJAX)

Several times I've been asked, or saw the question on the newsgroups, how to create a piece of javascript code which retrieves data from a webservice. This information has been included in the SDK and you'll be able to find it here:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/CrmSdk3_0/htm/v3d0accessingwebservices.asp

Here's the code example of that page:

// Declare variables.
var i=0; var j=0; var k=0; var r=0;
var serverUrl = "http://www.webservicex.net";

// This is the picklist.
switch (parseInt(event.srcElement.DataValue, 10))
{
case 1:
i = "JPY";
break;
case 2:
i = "GBP";
break;
case 3:
i = "EUR";
break;
}

// Instantiate at connection to the Web service and call the get method.
var xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");

xmlhttp.open("get", serverUrl + "/CurrencyConvertor.asmx/ConversionRate?FromCurrency=USD&ToCurrency="+escape(i), false);
xmlhttp.send();
var startTag = "<double xmlns=\"http://www.webserviceX.NET/\">";
var endTag = "</double>";
var exch;
var valueStart = 0;
var valueEnd = 0;

// Parse the returned XML string.
valueStart = xmlhttp.responseXML.xml.indexOf(startTag, valueEnd) + startTag.length;

valueEnd = xmlhttp.responseXml.xml.indexOf(endTag, valueEnd+1);
exch = xmlhttp.responseXML.xml.substring(valueStart, valueEnd);

// Set the Exchange rate on the custom attribute.
crmForm.all.fabrikam_exchangerate.DataValue = parseFloat (exch);
j = crmForm.all.totalamount.DataValue;
var kk = j*(parseFloat(exch));

// Calculate and set the total sum in the selected currency.
crmForm.all.fabrikam_totalcurrency.DataValue = kk;