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Select A Territory

-1

TerritoryDescription

TerritoryID

The createOptions() method iterates over each entry element in the XML and gets the text out of the optionText and optionValue elements via the getElementContent() helper method. The only thing particularly noteworthy about the getElementContent() method is that it uses the IE-specific text attribute of the XML element if it exists; otherwise it uses the W3C-standardized textContent attribute. Licensed to jonathan zheng

358

CHAPTER 9

Dynamic double combo

Error handling

We’re all finished. Almost. We’ve implemented all the behaviors needed to make this component fully operational. But, dang, we said we’d handle error conditions, too. You will recall that we have to implement a handleError() method in order to play nicely with the net.ContentLoader. So let’s implement that, and then we’ll really be finished. So what’s the appropriate recovery action if an error occurs? At this point we still can’t really say. The application using our DoubleCombo component ultimately should decide. Sounds like a job for our options object—remember the one we passed to the constructor? Let’s think about that contract for a second. What if we constructed our double-combo component with code that looks something like this?

function myApplicationErrorHandler(request) {

// Application function that knows how

// to handle an error condition

}

var comboOptions = { requestParameters: [

"param1=one", "param2=two" ], errorHandler: myApplicationErrorHandler }; var doubleCombo = new DoubleCombo( 'region',

'territory',

'DoubleComboXML.aspx',

comboOptions );

In this scenario, we’ve let the application define a function called myApplicationErrorHandler(). The implementation of this method is finally where we can put application-specific logic to handle the error condition. This could be an alert. Or it could be a much less intrusive “oops” message a la GMail. The point is we’ve deferred this decision to the application that’s using our component. Again, we’ve provided the mechanism and allowed someone else to provide the semantics. So now we have to write the DoubleCombo object’s handleError() method: handleError: function(request) {

if ( this.options.errorHandler )

this.options.errorHandler(request);

}

Component bliss

Congratulations are in order! We’re finally all done. We have a general component that we can construct with the IDs of any two select elements and some configuration information, and we have instant double-combo capability. And it’s just so … door slams open!

Licensed to jonathan zheng

Summary

359

Enter pointy-haired manager, 2:45 P.M. Friday. “Johnson,” he says. “We have to support subterritories! … And we need it by Monday morning!” Dramatic pause. “Ouch!” you finally retort. Then you regain your composure and say, “I’ll make it happen, sir. Even if I have to work all weekend.” He hands you the new page design:

Pointy-hair retreats. You open the HTML page in Emacs, because that’s the way you roll. You go directly to the head section. The cursor blinks. You begin to type:

You press a key that runs a macro to nicely format your code. You save. You exclaim over your shoulder, “I’ll be working from home,” as you pass by Pointy’s office at 2:57. You plop down on the sofa and think to yourself, “Boy, I am a rock star!” Okay, already. Enough of the fantasy.