Start Client Object Model

SharePoint 2007 allows using its Object model to run against server running SharePoint. For clients (not running SharePoint in the box) the simplest way to communicate with SharePoint server is web services. SharePoint Client Object Model (OM) can be run on client PC (where SharePoint is not installed) to communicate with SharePoint server. So whereas SharePoint (Server) Object Model runs in a SharePoint server and can manipulate SharePoint objects, Client OM can run in client PC and communicate with SharePoint server remotely.

SharePoint 2010 introduces three new client APIs which can be used to interact with SharePoint sites. The three APIs are targeted for three different types of clients:

1. For .net Managed applications (Eg: console applications, window applications, web applications).
• Application which are not running inside SharePoint Context 
• how to use Client OM from Managed .Net Client
2. For Silverlight applications.
3. For using with JavaScript (called ECMAScript or JSOM). 
• This API is only available for applications hosted inside SharePoint (for example, web part deployed in SharePoint site can use this JavaScript API for accessing SharePoint from browser using JavaScript).

Lets see  some basic problems SharePoint 2017 in absence of Client Object Model.

Why Client Object Model (OM)?

SharePoint 2007 had no Client Object model available. So you may ask why this is introduced in SharePoint 2010? We had no problem without Client OM and millions of sites are running smoothly without having Client OM. The main reason is that Microsoft has found lot of requests from SharePoint users to introduce more and more web services to get data out of SharePoint in the last couple of years. But introducing web services will not fix the issues, as Microsoft found, because then the request for more functionality in the web services will continue. Even if Microsoft provides a good numbers of web services with SharePoint, customization in web services will be required for different clients and this will make the out of the box web services unusable. Also introducing a large number of web services will be a waste as not all companies will use all the web services functionalities.

In response to add more web services from users, Microsoft has taken a different approach called Client Object Model (OM). This SharePoint Client OM will allow getting data out of SharePoint from PCs that are not hosting SharePoint. Also Client OM provides complete API to interact with SharePoint Server which is more intuitive and useful and very much similar with SharePoint Object Model.

Similarity with SharePoint Object Model

The Client OM familiar with SharePoint Object Model as below.

Server (Microsoft.SharePoint)	Client Object Model
SPContext	ClientContext
SPSite	Site
SPWeb	Web
SPList	List
SPListItem	ListItem
SPField	Field

So the class names in Client OM are similar as like SharePoint Object Model. However the way client OM will be used a bit different than usual SharePoint Object Model that we will explore in the upcoming posts.

How Client OM is developed and work under the hood?

It’s interesting how SharePoint team has developed the same set of classes for three different sets of applications (Managed, Silverlight and ECMAScript)

Client Type	Assembly/File
Managed Client	Microsoft.SharePoint.Client
Silverlight	Microsoft.SharePoint.Client.Silverlight
ECMAScript	SP.js or SP.debug.js

To ensure the same class object (say ListItem) behaves similarly in three different types of applications SharePoint team followed the steps described below:
a) SharePoint team first set attributes to the SharePoint classes and methods and properties that need to be exposed in Client OM.
b) Then a code generator is run against the SharePoint object model to generate client OM automatically.

This automated code generation has ensured maximum compatibility between these three sets of APIs. As the following figure shows client communicate to the server thorough Client OM which under the hood uses Client.svc WCF service to communicate with SharePoint Server. Client.svc service uses Server OM as per client request and return result to the client in JSON format.
Figure: How Client Object model works with Server
With this new Client OM, we almost don’t need to use web service to communicate with SharePoint server.
  
Client Object Model for JavaScript (ECMAScript)

Lets go through Client OM for JavaScript. ECMAScript Client OM is SharePoint 2010 client object model extension for using with JavaScript or JScript. Few points to notice about ECMAScript Client OM:

• ECMAScript object model can only be used in SharePoint sites. So you can’t use this object model in an asp.net site to access SharePoint resources deployed in another url as this is cross-site scripting and not allowed.
• You can’t use this object model in a SharePoint site to access resources in different SharePoint sites(i.e., different urls).
• You can use JQuery with ECMAScript Client OM by adding reference to JQuery.js.

• <SharePoint:ScriptLink Name="SP.js" runat="server" OnDemand="true" 
      Localizable="false" /> 

• You can use this ECMAScript Client OM in web part pages or application pages (aspx pages) by referencing a javascript file (SP.js). You don’t need to add reference to the file manually.
•  Rather use <SharePoint:ScriptLink Name=”sp.js” ………. />. 
• Location: “Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\TEMPLATE\LAYOUTS”
• To update with JavaScript, you need to add a FormDigest tag in your page for security purpose. I’ll explain it later in details. 
•  If your code modifies SharePoint content add a FormDigest control inside your page. The FormDigest add a security token inside your page based on user, site and time. Once the page is posted back the security token is validated. Once the security token is generated it’s valid for a configurable amount of time. Add the FormDigest inside <form>…</form> tag, as shown below:

• <SharePoint:FormDigest runat="server" />

 Use Client OM to retrieve data:
 

<script type="text/javascript">
    function getWebProperties() {
        var ctx = new SP.ClientContext.get_current();
        this.web = ctx.get_web();
        ctx.load(this.web);
        ctx.executeQueryAsync(Function.createDelegate(this, this.onSuccess),
            Function.createDelegate(this, this.onFail));
    }
    function onSuccess(sender, args) {
        alert('web title:' + this.web.get_title() + '\n ID:' + this.web.get_id() + 
            '\n Created Date:' + this.web.get_created());
    }
    function onFail(sender, args) {
        alert('failed to get list. Error:'+args.get_message());
    }
</script>

 Load minimal data if need:

1. ctx.load(this.web,'Title','Id','Created');

 Execute your JavaScript function after sp.js is loaded:

1.  ExecuteOrDelayUntilScriptLoaded(myjsfucntion, "sp.js");

 Update with ECMAScript Library:

<script type="text/javascript">
    function updateTitle() {
        var ctx = new SP.ClientContext.get_current();
        this.web = ctx.get_web();
        web.set_title('UpdatedTitle');
        this.web.update();
        ctx.executeQueryAsync(Function.createDelegate(this, this.onUpdate),
            Function.createDelegate(this, this.onFail));
    }
    function onUpdate(sender, args) {
        alert('title updated');
    }
    function onFail(sender, args) {
        alert('failed to update title. Error:'+args.get_message());
    }
</script>

Deployment Consideration

SharePoint provides two sets of JavaScript file: minified and unminified/debug version.

1. sp.js file is minified 
2. sp.debug is minified and debug version. 

The default master page in SharePoint has a scriptmanager in the page and whose ScriptMode is set to auto, as a result the minified version of js file loaded. If you want to use debug version you can add the
<deployment retail="false" /> in the <system.web> section of the web.config.

The ECMAScript supported in the following browsers:

• Microsoft Internet Explorer 7.0 or greater.
• Firefox 3.5 or greater
• Safari 4.0 or greater