Monads are all-the-rage these days in the JS world. I’d be surprised if any serious JS developer hadn’t heard of _Monads. _But just in case you haven’t, I like to describe a monad as a fancy box. It’s a special box. You can’t (well, you shouldn’t be able to) see exactly what’s inside the box, but you _can _know that this box holds values of a certain type, and exposes three primary operators with which we can modify or take out the content of that box. Those operations are what I call the Monad Interface.

OK, so _Monad _isn’t exactly an interface. But in JS we can think of it as one. As a quick refresher, in a strongly typed language (such as the C family) an _interface _is the definition of what a class object _has. _If you’ve ever used TypeScript, you know that an interface describes the expected shape of something — like an object, or the parameters and return value of a function. What an interface boils down to is a contract to be upheld by anything that implements that interface, but it gives no specifics of the implementation. It’s useful to think of things as interfaces, because interfaces are _abstract. _Abstraction is one of the most useful concepts in computer science. To say something is abstract is to express how far away it is from machine code. The further away from machine code we can be the better because humans brains understand the abstraction of _languages; _only machines are made to read machine code. The best part about an interface is that it is a cost-free abstraction. If you write one in TypeScript, for example, it doesn’t even generate code in the end, it only compile-time checks that the interface’s contract is upheld. In bare JS, an interface is only in the mind of the author. So we can only uphold an interface’s contract by assuring on our own that all of the expected methods and fields are correctly implemented — there are no compile time checks to help you out. But that’s OK, because the dynamically-typed nature of JS comes with some other very nice benefits, which I won’t necessarily discuss just this moment.

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