Confirming a Request before Submitting it to the Server

How to use JavaScript to verify a user request on the client (browser) before sending it to the server.

About this technique	Details
Category	HTML Client Techniques> JavaScript
Description	You'll learn about: Adding JavaScript to a page Writing JavaScript for a button click Handling a submit request
	You can run this technique code from: Database: Examples3_HTML Page: pgConditionalSubmit.html NOTE   First make sure that database is running on your localhost SilverStream Server
Related reading	See the chapter on advanced page topics in the Programmer's Guide

Adding JavaScript to a page   

The following describes how to add JavaScript code to a page.

1. Invoke the Properties dialog box of the page.

2. In the Page tab, select the Scripting field and click the Javascript button. This brings up the JavaScript editor.

Writing JavaScript for a button click   

The following code shows the JavaScript that launches a dialog box upon the Button1 button click.

  method handle_Button1_onClick() 
  { 
     if (confirm("Are you sure you want to execute this code?")) 
     {  
        Page.submit(this.Button1.name);  
     } 
  } 

Notes about the code

• The method must be named as shown so that it runs when the Button1 button is clicked.

• Display a Confirm dialog box with a message by calling confirm() and supplying the message string as the parameter. confirm() is a method of the Window object. This method returns true if the user selects OK; it returns false if the user selects Cancel.

• Send a Submit request to the server specifying the control for which the pageActionPerformed event should be fired. This line of code specifies that Button1 is the object whose pageActionPerformed event will be fired.

Handling a submit request   

The following code runs when a Submit request is processed by the server. This request was sent by the JavaScript when the user clicked the OK button in the Confirm dialog box.

  private void handle_Button1_pageActionPerformed(ActionEvent evt) throws Exception 
  { 
     Hashtable message = new Hashtable(); 
     message.put("MESSAGE", "You answered OK after you clicked Button1."); 
     message.put("URL1", "SilverStream/pages/pgConditionalSubmit.html"); 
     message.put("LINK1", "Return to pgConditionalSubmit.html"); 
     showPage("../../message.html", null, null, message); 
  } 

Notes about the code

• Create a Hashtable and provide the parameters for use by the message page.

• Redirect the request to the message.html URL. The bosrvletMessages servlet extracts the parameters, creates the message page, and redirects the request to it.