Dr. Dobb's Journal - November 2007 - (Page 50)

d11vaugh_p5db 9/17/07 8:37 AM Page 50 State of the Art TRANSPARENCY ON DEMAND Listing Four function LoadLib_XHR (LibName) { } function MyFunc () { MyOtherFunc (); } function Proxy () { LoadLib_XHR ("MyLib.js"); // Load synchronously using XHR this["MyFunc"] = OriginalRef; // Replace the ref here in case // MyFunc is recursive return OriginalRef.call (this, arguments); } var OriginalRef = this["MyFunc"]; this["MyFunc"] = Proxy; // Intercept is set at a distance // from clients of MyFunc MyFunc (); // Call routed through Proxy, // library is loaded transparently MyFunc (); // Call is now entirely conventional // -- Contents of MyLib.js function MyOtherFunc () { } interception, it allows (among other things) unlimited numbers of affixes for a given function, with fine control over their type, number, longevity, and execution order. In deference to a venerable tradition, therefore, Listing Six (available online) demonstrates loading a JavaScript library transparently on demand using AspectJS. This uses the AddPrefix method of a singleton object called AJS to set up the interception. The first two parameters signify the OnMouseClick method of the global object as the interceptee, and the third specifies LoadLib_XHR as the prefix. The fourth is an optional parameter that is passed to the prefix—in this case the name of the library to be loaded—and the final argument specifies that the prefix should be removed after just one execution. The net result is that clicking on the client area of the browser’s window causes Hello.js to be loaded, thus allowing a customary greeting to be displayed. An Open Door Resolving the downside to on-demand JavaScript lets you exploit its full potential, and generalizing the solution opens the door to a wealth of aspect-oriented techniques. Consolidating the principles of function interception in a reusable library lets you affix methods arbitrarily to virtually any function call. This permits the serious application of AOP techniques to professional web development, thus allowing remote tracing, debugging, and error reporting, along with client-side performance measurement, user-interaction modeling, and others that, as yet, are only a twinkle in the developer’s eye. DDJ 50 Dr. Dobb’s Journal l www.ddj.com l November 2007 http://www.scitools.com http://www.scitools.com http://www.ddj.com

Table of Contents Feed for the Digital Edition of Dr. Dobb's Journal - November 2007

Contents Hmmmm Alia Vox Developer Diaries Developer’s Notebook Smart Compilers - But Smart Enough? Conversations Grid-Enabling Resource-Intensive Applications Distributed Computing: Windows and Linux Adobe AIR: Desktop/Web Convergence Transparency on Demand Reusable Associations Effective Concurrency The Agile Edge Swaine’s Flames

Dr. Dobb's Journal - November 2007

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