Hyper Cloud Functional JS with Deno, 1 Mar 2021

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From YouTube: Either-This-or-That

Description

This screencast is about the Either data type. https://blog.hyper63.com/either-this-or-that/

A

Hello in this screencast we're going to talk about either either this or either that either is a data type that basically allows you to make safe functions. So you can, you know, run some function and if it returns an error, you can use an either function to return either a left or a right and through your pipeline right will continue down. The pipeline left will exit out of the pipeline.

A

So I'm going to show a few examples of that: we're going to use uh deno or dino and an either library and some ramda.

A

So basically, with an ether, you can create a functional pipeline and we'll start that with here, with an of so we're going to initialize the value either dot of and we'll just put a value 1 in, and then we can fold that out of the container so either is a data type that contains a value and you can manipulate it.

A

So the first thing we'll do is just kind of fold that out and it's either going to return a left which this function handles the left side and we'll just do console log left and then the value and the second function is the right. So we will console log that with the right and return the value and if we run that we should get one, because the default of the of is a right instance. So it'll always return the right. Now.

A

If we want to, let's say, add, um add to this value, you know we can map over it. So, let's um pull in, add and and go ahead and pull in multiply uh from ramba and then we'll just map, and what map does is allows you to run a function inside the container.

A

So we can run the the add function and give it a one and that'll just add one to whatever the value is. So if we run that, um let's see.

A

Restructuring initial answers.

A

A

That's it so if we run that, then we get two right and if we map over another function, let's say multiply by two and we run that we get a right of four. um So so that's basically how either works a lot. You know as any kind of functional type. You can create a pipeline, we call map or chain, and then you can fold at the end and it's gonna return um the value that's inside that container.

A

um So what if this value is null right so um or if it's not a number, so the add and the multiply functions is kind of expecting it to be a number. So if it's not a number, that's not good. So we need to do a check to make it safe right. So we can create a function down here called is number it takes a value and then basically it's just gonna say: if is number, then we want to return the value, uh the right of the the value right.

A

So we want to return a new either with the value and then, if it is not a number, then we want to return left and we'll just say not a number. But we could kind of put any kind of value in here and what's going to happen is when this runs we're going to chain and the reason we're going to use chain is this function is going to return another either and that either can be either a right or a left. So it's kind of like a flat map.

A

So what we're going to do when we chain is call is number and then it's going to return a new ether that can either proceed down the pipeline or it will kind of pass the maps and and go to this fold left function. So let's run that and if everything works great then we should get four again.

A

uh Let's see right's not defined cool, so let's bring in right and left from either okay and we get four. So what happened? Is we checked if the value in the container is a number? And if so, then we'll run the maps um and let's make it not so so, let's make it a null right and when we run that we get left is not a number. So what happens? Is this chain returns a left and the either says?

A

Okay, I'm not doing a map not doing a map, and then, when we come to fold, I'm going to run the left function in the fold and that's basically how it either works um now with either um you can get a couple of common methods to make things just a little bit easier.

A

One is called from nullable.

A

And the other is called try catch so with from noble I'm just going to clear out.

A

A

With from nullable, it basically takes a value and either returns a left or right. If the value is null, it returns a left. If the value is not null, it returns a right. So we can test that here with either.

A

And put a null in and then we can chain from nullable and we can just do a fold and.

A

Is null, and then just do is not no right.

A

If we run that we get is null, but if I put a value in here, we get is not null. If I put undefined, we get is null so from noble can basically allow you to check um you know a value coming from somewhere. Maybe you can't control and make sure that it's not null before you get into your your business logic.

A

Let's look at try catch, try catch takes a function and then it's going to run that function and if that function throws an error, then it's going to run a return, a lift. If the function doesn't throw an error, it will return the result of that function as a write. So we can test that out by just doing try catch and just putting a function in here and we'll just go ahead and throw a new error.

A

Catch me. If you can so this function is going to throw an error so, but but but the either is going to catch that error and then it's going to return either a left or right so it'll kind of make this function safe. So we can fold and.

A

He got me so the left means that uh it found an error and and it caught it and it returned it as a left and then the right.

A

Let's just do no error right, so if we run that we should get you got me, we we had an error um and we can get access to that error right. So when it does throw the air we can get access to it and write it out.

A

So, that's it that's the basics of the either you have kind of map and chain which you can create your your pipeline, and then you have fold. You also have an extract function which will return the value as a result when you call in either pipeline.

A

So those are the basic methods in the description I'll attach the blog to check out more details about it, but basically either can really help you manage null values or errors within your pipelines to make sure your business logic is safe and thank you for.