In recent years, development practices have moved to a more functional style of programming. This means less focus on mutable programming (changing variables instead of creating new ones when we want to modify something). Mutability happens when we change a variable from one thing to another. This could be updating a number, changing what the message says, or even changing the item from a string to a number. A mutable state leads to quite a few areas of programming pitfalls, such as undetermined state, deadlocking in multithreaded environments, and even the changing of data types when we did not mean to (also known as side effects). Now, we have many libraries and languages that help us curtail this behavior.
All of this has caused a push toward the use of immutable data structures and functions that create new objects based on the input. While this leads to fewer errors in terms of mutable state, it presents a host of other issues, predominantly, higher memory usage and lower speeds. Most JavaScript runtimes do not have optimizations that allow for this style of programming. When we are concerned with memory and speed, we need to have as much of an advantage as possible, and this is the advantage mutable programming gives us.
In this chapter, we are going to focus on the following topics:
- Current trends with immutability on the web
- Writing safe mutable code
- Functional-like programming on the web
