In the last chapter, we discussed the purpose that sits at the very beginning of a piece of code: solving a problem for a user. We discussed the difficulties of catering to both the machine and the human. We reminded ourselves that, at its core, writing code is about communicating intent.

In this chapter, we will derive four core tenets from those foundations that are necessary to think about when creating software. These tenets are reliability, efficiency, maintainability, and usability. A good piece of software can be said to have all of these qualities. A bad piece of software can be said to have none of them. Crucially, however, these tenets are not rules. Instead, it is useful to see them as lenses through which you can look at your code. For each tenet, we will discover why it is important through a mix of analogies and JavaScript examples. You should come away from this chapter with an ability to apply these tenets to your code.

Specifically, we will be covering the following tenets:

• Reliability
• Efficiency
• Maintainability
• Usability