Mastering JavaScript Functional Programming - Second Edition

Calling a function – the Try monad

If we are calling functions that may throw exceptions and we want to do so in a functional way, we could use the Try monad to encapsulate the function result or the exception. The idea is basically the same as the Either monad: the only difference is in the constructor, which receives a function and calls it:

• If there are no problems, the returned value becomes the right value for the monad.
• If there's an exception, it will become the left value.

This can be seen in the following code:

class Try extends Either {  constructor(fn, msg) {    try {      return Either.of(null, fn());    } catch (e) {      return Either.of(msg || e, null);    }  }  static of(fn, msg) {    return new Try(fn, msg);  }}

Now, we can invoke any function, ...