Bad Design Assures Bad Results
I’ve not read JavaScript Application Design yet, but was struck by the correctness of a statement made in “About the Book”:
The fate of most applications is often sealed before a single line of code has been written.
As I’ve blogged about before, all to often team lurch into code well in advance of actually understanding the problem they are attempting to solve, and lacking any sensible architecture and process.
Good design and effective processes are the foundation on which maintainable applications are built, scaled, and improved.
Tales from a Trading Desk 
Proper planning and preparation prevents p1ss poor performance….
However building a minimal viable product early is a great way to learn about the problem