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How to call a web method by JavaScript

I didn’t get a time to write something here for a long time. Yes I can say I was busy. (But I was not :)) Anyway I thought to write about something finally and I promise (this is a serious promise) that I will try to do something (do a posting actually) on my blog more frequently.
The ability to call the web methods by JavaScript on .net is very very useful and we can implement the web pages more efficiently by using this. For example we do not need to send whole page and update. Yes this is AJAX (that what I think).
Here is a web method example. It should be on the aspx page code behind and should be a static (shared) method. I have tried to insert the web methods on user controls and was unable to do so (if you know a way please share with us). This is on VB.net.
 _
 Public Shared Function GetMyData(ByVal studentID As Integer, ByVal schoolID As Integer) As Student
        Dim studentService As New StudentService()
        Dim result As Student = studentService.GetStudent(studentID, schoolID)
        Return result
    End Function

GetMyData method will create a Student entity based on the IDs passed in and this method can even call to DB to get the data (since this is on server side we can do anything).
Then this method (GetMyData) needs to be executed by JavaScript. Here is the example on how to do that.
this.GetStudent = function(args)
    {        
        PageMethods.GetMyData(_studentID, _ schoolID, _this.UpdateStudentFields, _this.ServiceError);
    }

In here if you have noticed I have send 2 more parameters (_this.UpdateStudentFields, _this.ServiceError) than the web method accepts. (Was not by any mistake:))
_this.UpdateStudentFields – is the JavaScript method name that will execute when we returned from the web method. So basically what happens is Student entity will be passed into this method (UpdateStudentFields) as the result. So then we can do anything by JavaScript by using this result entity.
this. UpdateStudentFields = function(result)
    {        
        if (result.Succeeded)
        {
        //assign the values to the fields
        //studentname = result.Name;
        }
    }

_this.ServiceError – this is the javascript method name that executes if there were any exceptions. So then we can do anything even with the error (exception actually). I prefer to show the errors to the end user (swallowing exeptions is not a good practice).
this.ServiceError = function(error)
    {
       //this will show the error on page
// AddError method should be implimented to do so … 
        AddError(error.get_message());
    }

Hope this was helpful and if there is any issues or if you know a better way to impliment this please leave a comment.

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