An Introduction to AJAX Techniques and Frameworks for ASP.NET

var itemList, itemQuantityDisplay, progressDisplay;

function onCallbackComplete(result){
    progressDisplay.style.display = "none";

    itemQuantityDisplay.className = "";
    itemQuantityDisplay.style.display = "";
    itemQuantityDisplay.innerHTML = result + " in stock";
}

function onCallbackError(){
    progressDisplay.style.display = "none";

    itemQuantityDisplay.className = "Error";
    itemQuantityDisplay.style.display = "";
    itemQuantityDisplay.innerHTML = "Error retrieving quantity";
}

function itemList_OnChange(){
    progressDisplay.style.display = "";
    itemQuantityDisplay.style.display = "none";
    
    PageMethods.GetItemQuantity(onCallbackComplete, onCallbackError, onCallbackError);
}

Sys.Runtime.load.add(function() {
    itemList = document.getElementById("ItemList");
    itemQuantityDisplay = document.getElementById("ItemQuantityDisplay");
    progressDisplay = document.getElementById("ProgressDisplay");
    
    itemList.attachEvent("onchange", itemList_OnChange);
});