Details are here:
If a function may not return with a value, it might be a good idea to wrap it in an Either. In functional programming, the Either monad is a special abstract data type that allows you to attach two different code paths: a success path, or a fail path. JavaScript has a built-in asynchronous Either monad-ish data type called Promise. You can use it to do declarative error branching for undefined values:
const exists = x => x != null;
const ifExists = value => exists(value) ?
Promise.resolve(value) :
Promise.reject(`Invalid value: ${ value }`);
ifExists(null).then(log).catch(log); // Invalid value: null
ifExists('hello').then(log).catch(log); // helloYou could write a synchronous version of that if you want, but I haven’t needed it much. I’ll leave that as an exercise for you. If you have a good grounding in functors and monads, the process will be easier. If that sounds intimidating, don’t worry about it. Just use promises. They’re built-in and they work fine most of the time.
Details are here:
If a function may not return with a value, it might be a good idea to wrap it in an Either. In functional programming, the Either monad is a special abstract data type that allows you to attach two different code paths: a success path, or a fail path. JavaScript has a built-in asynchronous Either monad-ish data type called Promise. You can use it to do declarative error branching for undefined values:
You could write a synchronous version of that if you want, but I haven’t needed it much. I’ll leave that as an exercise for you. If you have a good grounding in functors and monads, the process will be easier. If that sounds intimidating, don’t worry about it. Just use promises. They’re built-in and they work fine most of the time.