Architecture of a single-page JavaScript web application?

MVC architecture of PureMVC/JS is the most elegant IMO. I learned a lot from it. I also found Scalable JavaScript Application Architecture by Nicholas Zakas helpful in researching client side architecture options.

Two other tips

1. I've found view, focus, and input management are areas that need special attention in single page web apps
2. I also found it helpful to abstract away the JS library, leaving door open to change mind on what you use, or mix & match should the need arise.

The way I build apps:

• ExtJS framework, single page app, every component defined in a separate JS file, loaded on-demand
• Every component contacts its own dedicated web service (sometimes more than one), fetching data into ExtJS stores or special-purpose data structures
• The rendering uses standard ExtJS components, so I can bind stores to grids, load forms from records, ...

Just choose a javascript framework, and follow its best practices. My favorites are ExtJS and GWT, but YMMV.

Do NOT roll your own solution for this. The effort required to duplicate what modern javascript frameworks do is too big. It is always faster to adapt something existing than to build it all from scratch.

Question - What makes an application complex ? 

Answer - The use of word 'complex' in the question itself. Hence, a common tendency will be to look out for a complex solution right from the beginning.

Question - What does the word complex means ?

Answer - Anything that is unknown or partially understood. Example : The theory of Gravity even today is COMPLEX to me but not to Sir Isaac Newton who discovered it in 1655.

Question - What tools can I use to deal with complexity ?

Answer - Understanding and simplicity.

Question - But I understand my application . Its still complex ?

Answer - Think twice, because understanding and complexity does not co-exist. If you understand a huge huge application, I am sure you will agree that it is nothing but an integration of small and simple units.

Question - Why all of the above philosophical discussion for a question on 
           Single Page Application (SAP)?

Answer - Because,

-> SPA is not some kind of core technology that is newly invented for which we need to reinvent the wheel for a lot of things that we are doing in application development.

-> Its a concept driven by the need for better performance, availability, scalability and maintainability of web applications.

-> Its a fairly newly identified design pattern, so an understanding of SPA as a design pattern goes long way in making informed decisions about the architecture of a SPA.

-> At the root level no SPA is complex, because after understanding the needs of an application and the SPA pattern, you will realize that you are still creating an application, pretty much the same way you did before with some modifications and re-arrangements in the development approach.

Question - What about the use of Frameworks ?

Answer - Frameworks are boiler plate code / solution for some commonly identified and generic patterns, hence they can take off x% (variable, based on the application) load from application development but then not a lot should be expected out of them specially for heavy and growing applications. Its always a good case to be in complete control of your application structure and flow but most importantly the code for it. There should be no grey or black areas in the application code.

Question - Can you suggest one of the many approaches to SPA architecture ?

Answer - Think of your own framework based on the nature of your application. Categorize application components. Look for an existing framework that is close to your derived framework, if you find it then use it, if you do not find it then I suggest going ahead with your own. Creating framework is quite an effort upfront but produces better results in long run. Some basic components in my SPA framework will be:

• Data Source : Models / Collections of Models

• Mark Up for presenting data : Templates

• Interaction with the application : Events

• State capturing and navigation : Routing

• Utilities , widgets and plug-ins : libraries

Let me know if this helped in any way and good luck with your SPA architecture !!

Nicholas Zakas's presentation as shared by Dean is a very good place to start with. I was also struggling to answer the same question for a while. After doing couple of large scale Javascript products, thought of sharing the learnings as a reference architecture in case someone needs it. Have a look at:

http://boilerplatejs.org/

It addresses common Javascript development concerns such as:

• Solution structuring
• Creating complex module hierarchy
• Self contained UI components
• Event based inter module communication
• Routing, History, Bookmarking
• Unit Testing
• Localization
• Document Generation

etc.