Background

One of the coolest features of SharePoint 2010 is Client Object Model. You might already know that if we have to talk to SharePoint 2007 and don’t want to write the server side code then we call SharePoint Web Services. Now with SharePoint 2010 we can use Client Object Model to talk to SharePoint and the option of web services is still there. Once a wise man said, two options are always better than one.

How SharePoint Client Object Model Works

SharePoint Client Managed Object Model is a SharePoint API that runs on the client side. It converts the API calls made by the application, into XML request and sends it to the SharePoint server. On the server, the XML request is handled by a service called Client.svc where it translates the XML request in to appropriate Object Model calls (SharePoint Server Object Model) and gets the results. After getting the results, Client.svc translates them into JavaScript Object Notation (JSON) and sends back to the Client Managed Object Model. On the client side the JSON response is translated into ECMAScript objects for ECMAScript.

Ref1: http://msdn.microsoft.com/en-us/library/ee538253.aspx
Ref2: http://msdn.microsoft.com/en-us/library/ee857094(office.14).aspx

Writing the ECMAScript

1. Create a list called Product and add few items in it.
2. Create a test ASPX page in the Pages library.
3. Add the Content Editor web part and add the following script in it.

<script type="text/javascript">
ExecuteOrDelayUntilScriptLoaded(MainFunction, "sp.js"); 
var objContext = null; 
var objWeb = null     
var objList = null;
var objItem = null;
    function MainFunction() {   
        objContext = new SP.ClientContext.get_current();
        objWeb = objContext.get_web();   
        objList = objWeb.get_lists().getByTitle("Product");
        objContext.load(objList);
        objContext.executeQueryAsync(Function.createDelegate(this, this.onSuccess), Function.createDelegate(this, this.onFail));   
    }   
    function onSuccess(sender, args) {
        alert('Item Count: ' + objList.get_itemCount());
    }   
    function onFail(sender, args) {   
        alert('Some error has occured.');   
    }  
 </script>

Explanation

To load the Java script Client Object Model, we have to call ExecuteOrDelayUntilScriptLoaded(Func, "sp.js") . This function takes the name of the function that need to be executed as a main function and will load the SP.js file, which is the core of Client Object Model. We have to load the current context in order to play with the site content by SP.ClientContext and then get the current site by calling get_web() function of current context. After getting the current site we call getByTitle to get the Product list and then we loaded that list. Note that we are not loading all the objects but only the list. Loading all the objects will cause delay and performance issues. We are loading the list asynchronously and if the call is successful OnSuccess()will be called and if the call failes OnFail() will be called.

Conclusion

ECMAScript is a java script based client side scripting language which is now supported in SharePoint 2010 and can be used to access Client Object Model. Users can write ECMAScript in an ASPX page for SharePoint 2010 sites and can manipulate the SharePoint content without even touching the Visual Studio (or SharePoint Designer) and getting involved in the complexities of the web services.