Don't Side-step TypeScript - a podcast by Kent C. Dodds

Hello everyone So today I'm going to talk about TypeScript and tricking
type script versus fixing your code So, you know, the the null non-nullassertion thing where you put the exclamation point at the end of something
to say, hey type script this isn't going to be no or whatever.
I don't really use that. There's actually two reasons. One of them is
because it looks like when you're looking at the code that looks like
that's a feature of JavaScript, but it's not and so I don't really like
using things that look like they could be a feature of JavaScript butaren't I don't know maybe that's just weird of me.
But the the biggest reason is that most often if TypeScript thinks thatthis can be null it's most likely that it actually can be no and and you
could put that bang there or you can do type assertions or casting andwhatever but it's I I don't like telling TypeScript that no this like this
won't be this value when it actually could be that value.
So I'm thinking about a specific example that my friend Peter on discord on
during office hours today brought up and I was.Live streaming and I wasreading a value out of local storage and and then parsing that with JSON
down parse. And JSON parts can technically accept anything and then itstringifies it and so you can pass it null it will stringify it to null and
the result will be null.Sorry, it will stringify it to the string of null and then the result of
parsing that will be no. And so yeah, you can just pass in no but thetypescript definitions for that except specifically a string. It has to be
a string that you pass to it. Even though you can technically pass anythingand it'll just get stringified automatically.
So,What I did was I did the double question marks, whatever that's called
the I can't remember what that operator is called but yeah. So I'd say okay
read in the locust storage if that's null then it will just pass in the
string of null and then that will result in an old value.And he suggested that oh why don't you just do a bang on that on the end of
that and then that should work just fine just say, you know, hey typescript this is not going to be null, but it actually will be it'll just be
okay that it'll be null.
And so,But he also suggested you could also just pass it to the stringconstructor and then that would stringify null and then you could pass it
in And I opted for passing it tothe string constructor because I don't
want to tell TypeScript that this will never be this null value.What it actually will be in reality. And so it's not just communicating to
TypeScript. It's also communicating to the other people who are going to be
reading the code. So anyway, I hope that's sort of useful and train of
thought try not to convince. TypeScript that something will not be of acertain type what it actually could be.
Hope you're having an awesome day, we'll see you all next time.

Further episodes of 3 Minutes with Kent

Further podcasts by Kent C. Dodds

Website of Kent C. Dodds