Refreshing only part of your Web Page

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Background

I needed to make a portion of Web Page to refresh without refreshing the entire page. Everytime I tried, it would always refresh the entire page. I got very frustrated, then I read an article from CodeProject (CodeProject Discussion Boards) and thought I would talk to Uwe Kein (the Author) about this. His suggestion was to use Remote Scripting which by the articles I read was the way to go. Unfortunately, my company didn't have that installed on their dev or production systems. I couldn't wait for them, so I tried scriptlets. After a lot of trial and error, I got it to work. I am writing this article to try and help anyone else in this situation.

What will this do for you?

Show you how to refresh a scriptlet every second using a timer inside the scriptlet. This example uses a DNS-Connection-less (meaning you don't have to create a System DNS entry through ODBC) way to access the MS-Access database, but you can adapt it to any other by changing the ConnectionString (see below formats):

//Build the connection string
//
//ConnectionStringFormat(seebelow):
//ConnectionString="DRIVER=SQLServer;SERVER=MySQLServer;CATALOG=MyDatabase;UID=USERID;PWD=Password";
//
//forSQL7.0:
//ConnectionString="DRIVER=SQLServer;SERVER=TopTen;CATALOG=TopTen;UID=TopTen;PWD=TopTen";
//
//for Access Database (on Server):
//ConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Persist Security Info=False;" &_
//                   "Data Source=\\\\SERVER\\Share\\directory\\TopTen.mdb";
//
//for Access Database (on local drive):
//ConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Persist Security Info=False;" &_
//                   "Data Source=C:\\Database\\TopTen.mdb";

I have included an Access2000 Database called/Located at C:\TopTen\TopTen.mdb to use for the example, or you can use the text file TopTen.txt which will create a Table, User Login, User Role, Primary Key, and Insert ten rows for an SQL 7.x database.

Note: if you want to use ASP (server calls) code, write it as a "JavaScript" function and use RUNAT=server in the <SCRIPT> Tag.

What are scriptlets

Scriptlets are HTML pages that heavily exploit the DHTML object model. Here is how simple it is...write a normal HTML file. Create an function for the scriptlet called "CreatePage". Now, create a "new" object called public_description and assign it the result of the function. This function works as a the constructor of the scriptlet object. In one sense, the public_description variable is like a header file for a C++ class. It defines all the properties and methods that the scriptlet exposes. See the example below:

// declare the object interface (constructor)
public_description = new CreatePage();
var InScriptlet = (typeof(window.external.version) == "string");

// set some variables
mEnabled = 1;
mTimer = 0

function CreatePage() {
	this.Refresh = Refresh;
	this.Enable = Enable;
}

Since a scriptlet is an HTML or ASP page (and can also be displayed as a stand-alone document), you might occasionally incur a system error due to a property or a method that IE 4 (or higher) doesn't find. This only happens if your scriptlet attempts to access its parent environment. To work around this you need a way to detect whether a given page is viewed as a scriptlet or not. Since the external object gets initialized if, and only if, an HTML page is running as a scriptlet, provide a boolean variable as a safeguard and access the external object only when it is absolutely safe to do so.

var InScriptlet = (typeof(window.external.version) == "string");

The variable above InScriptlet will contain True or False, according to the type of the property external.version (current version of the scriptlet engine). You can now use InScriptlet in your code to determine how the page is being viewed.

The way to get it to refresh is either by calling the "Refresh" method or by setting a timer in the window.onLoad event:

mTimer = window.setInterval( "DoUpdatePage()", 1000, "VBScript" )

Since both ActiveX controls and scriptlets are inserted through the same tag <OBJECT>, you need to make the browser distinguish between them (see below).

ActiveX Control:

<OBJECT>
  id="Button1"
  classid="..."
  width="..."
  height="..."
  <param name="...">
</OBJECT>

Scriptlet:

<OBJECT>
  id="TopTen"
  data="TopTen.htm"
  width="..."
  height="..."
  type="text/x-scriptlet"
</OBJECT>

Acknowledgements

For a good book/examples check out Scriptlets and for the examples in the book, go to Examples