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Using JavaScript callback functions

From: ColdFusion 9 Essential Training

Video: Using JavaScript callback functions

The term Ajax stands for Asynchronous JavaScript and XML. Asynchronous means that instead of responding synchronously, that is launching a bit of code and waiting for a response, you deal with user and data events asynchronously, setting up listeners that deal with events when they happen. You can respond to clicks on the Message Box produced by ColdFusion by creating a function that will be called when the clicks happen. These kinds of functions are known as callback functions.

Using JavaScript callback functions

The term Ajax stands for Asynchronous JavaScript and XML. Asynchronous means that instead of responding synchronously, that is launching a bit of code and waiting for a response, you deal with user and data events asynchronously, setting up listeners that deal with events when they happen. You can respond to clicks on the Message Box produced by ColdFusion by creating a function that will be called when the clicks happen. These kinds of functions are known as callback functions.

You create the function and you set it up to be called the way the Message Box knows how to call it and then you add a bit of code to link it all together. I'm still working in the index.cfm file, in the photographers directory of the application. I'll start by creating a function that will be called when the user clicks either the Yes or the No box on the MessageBox component. I will name my new function doDelete. Because this is going to be set up as a callback function for the MessageBox component, it will be called in a certain way.

It's going to be passed a parameter and the parameter's value will be the name of the button that was clicked in lowercase. I will name this parameter btn. Then I will create a pair of curly braces and within the function I'm going to use an alert method and just output the value of that parameter or argument that was passed in, btn. So now, to test that function I'll go down to the cfmessagebox tag. In the cfmessagebox tag I'll add a new attribute named callbackhandler.

The callbackhandler attribute gets set to the name of the function that you want to call, doDelete. This is a JavaScript function, so it is case-sensitive. You must spell it here exactly the same as how you spelled it when you defined it in the scripting section. Notice that you don't add any parentheses or pass any values at this point. When the function is called by the MessageBox component, the button variable will be passed correctly. Now to test all this, I'll run the page in an external browser.

I will click on one of the links for a photographer and I will see the confirmation message. I will click the yes button and I will see feedback that the value of btn is yes. Notice that the word yes comes back in lowercase, even though I spelled it in uppercase. That will be important to know when we want to evaluate what the user did. I will click OK to clear the JavaScript dialog and I will click another delete link and this time click No and I get back a value of No.

So that's how callback functions work in the world of Ajax and in the world of the new ColdFusion Ajax tools such as the ColdFusion MessageBox component. Represented here with the cfmessagebox tag and activated by the call to ColdFusion.MessageBox.show. The doDelete function will now be responsible for responding to when the user clicks one of the two buttons and I'll finish this entire workflow in the final video of this chapter.

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ColdFusion 9 Essential Training

95 video lessons · 9703 viewers

David Gassner
Author

 
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  1. 5m 54s
    1. Welcome
      1m 24s
    2. Using the exercise files
      2m 50s
    3. Overview
      1m 40s
  2. 35m 16s
    1. Understanding application servers
      7m 3s
    2. Installing ColdFusion 9 on Windows
      5m 28s
    3. Installing ColdFusion 9 on Mac OS X
      6m 20s
    4. Completing the Configuration wizard
      1m 50s
    5. Starting and stopping ColdFusion on Windows
      4m 7s
    6. Starting and stopping ColdFusion on Mac OS X
      2m 37s
    7. Installing ColdFusion Builder on Windows
      4m 13s
    8. Installing ColdFusion Builder on Mac OS X
      2m 1s
    9. Setting folder permissions on Mac OS X
      1m 37s
  3. 45m 34s
    1. Using Eclipse perspectives and views
      5m 42s
    2. Defining a ColdFusion server
      8m 42s
    3. Creating a ColdFusion project
      4m 40s
    4. Creating and browsing a ColdFusion page
      5m 36s
    5. Defining a default page template
      3m 58s
    6. Setting and outputting variables
      7m 55s
    7. Using the Snippets view
      4m 49s
    8. Using an external browser
      2m 8s
    9. Using online help
      2m 4s
  4. 35m 48s
    1. Adding numbers and concatenating strings
      8m 7s
    2. Using Debug Output
      6m 10s
    3. Inspecting variables with ‹cfdump›
      4m 54s
    4. Using arrays
      5m 21s
    5. Using structures
      3m 51s
    6. Configuring the line debugger
      1m 25s
    7. Using the line debugger
      6m 0s
  5. 53m 45s
    1. Scripting an Apache Derby database
      3m 34s
    2. Defining a data source in ColdFusion Administrator
      6m 13s
    3. Exploring data sources in RDS Dataview
      4m 2s
    4. Using SQL and the ‹cfquery› tag
      6m 58s
    5. Outputting data from a query object
      4m 2s
    6. Outputting a dynamic HTML table from a query
      7m 0s
    7. Generating alternating row colors
      6m 55s
    8. Creating an application directory and home page
      5m 26s
    9. Displaying data on the home page
      5m 43s
    10. Redirecting requests with ‹cflocation›
      3m 52s
  6. 32m 17s
    1. Including pages with ‹cfinclude›
      4m 21s
    2. Creating reusable header and footer files with ‹cfinclude›
      4m 39s
    3. Creating and calling custom tags
      3m 8s
    4. Passing data into custom tags
      2m 34s
    5. Setting default values for custom tag attributes
      4m 51s
    6. Calling custom tags with ‹cfmodule›
      3m 54s
    7. Using a custom tag as a website header
      3m 55s
    8. Creating an application template file
      4m 55s
  7. 52m 6s
    1. Creating a ColdFusion Component (CFC)
      5m 6s
    2. Declaring CFC functions
      3m 28s
    3. Calling CFC methods with ‹cfinvoke›
      2m 28s
    4. Using CFC properties
      4m 51s
    5. Passing data into functions
      3m 38s
    6. Creating and calling CFCs with script syntax
      5m 25s
    7. Generating data access CFCs in ColdFusion Builder
      4m 35s
    8. Calling generated data access methods
      7m 41s
    9. Creating a dynamic HTML table from an array
      8m 8s
    10. Creating an Application.cfc file
      3m 11s
    11. Using an application data source variable
      3m 35s
  8. 32m 56s
    1. Generating an ORM map component
      7m 58s
    2. Enabling an application to use ORM
      1m 58s
    3. Retrieving data with ORM
      2m 55s
    4. Generating mappings for multiple tables
      4m 22s
    5. Filtering data with ORM
      5m 35s
    6. Displaying result data with a custom tag
      10m 8s
  9. 27m 58s
    1. Passing URL variables in hyperlinks
      6m 13s
    2. Passing multiple URL variables
      2m 50s
    3. Encoding URLs with URLEncodedFormat()
      4m 12s
    4. Checking for available variables with isDefined()
      2m 41s
    5. Creating a data-driven hyperlink
      5m 4s
    6. Displaying selected data in a detail page
      6m 58s
  10. 40m 36s
    1. Using HTML data entry forms
      6m 53s
    2. Processing form variables
      3m 24s
    3. Creating self-posting forms with ‹cfform›
      4m 40s
    4. Creating a search interface
      3m 9s
    5. Processing complex queries with HQL
      8m 53s
    6. Creating a dynamic pulldown list with ‹cfselect›
      7m 16s
    7. Displaying form results
      6m 21s
  11. 43m 46s
    1. Building a data entry form for managing data
      5m 15s
    2. Preparing an ORM mapping for inserting data
      3m 47s
    3. Inserting data with ORM
      5m 23s
    4. Retrieving data for an update form
      4m 16s
    5. Populating form controls with existing data
      5m 2s
    6. Updating data with ORM
      2m 56s
    7. Confirming actions with an Ajax message box
      7m 22s
    8. Using JavaScript callback functions
      3m 15s
    9. Deleting data with ORM
      6m 30s
  12. 9m 37s
    1. Defining client-side form validation rules
      4m 14s
    2. Validating on the server with custom CFML
      5m 23s
  13. 18m 9s
    1. Using the Application.cfc onRequest() method
      4m 12s
    2. Creating and using a login form
      4m 53s
    3. Authenticating users with ‹cflogin›
      6m 1s
    4. Logging out users
      3m 3s
  14. 7m 11s
    1. Configuring an FTP site
      2m 27s
    2. Setting a ColdFusion project's synchronization connection
      2m 17s
    3. Uploading files to the production server
      2m 27s
  15. 46s
    1. Goodbye
      46s

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