Union vs. intersection types

[nyfarn]

Is your feature request related to a problem? Please describe.
If I'm not mistaken, the Basics code example under "Intersection types" actually shows a union type and vice versa.
Cf. https://www.typescriptlang.org/docs/handbook/advanced-types.html

Describe the solution you'd like
The headings could be swapped.

Thank you for this great course.

[mike-north]

Good catch! unfortunately I can't change the notes since we've already recorded the course and can't allow the video and code to get out of sync. Definitely something to ensure we get right in the next version!

[nyfarn]

Sure, that makes sense. Thank you!

[umar-khan]

Would it be possible to have a note saying that the Intersection and Union notes should be swapped? It might help future students at least until a v3 is up.

I've seen other courses have little helpful popups which show up as blue sections on the video timeline. Eg.

[hatched-esther]

Wow.. Im here because I was like... this does not make sense hahah glad to find that Im not crazy.

[paseaf]

Actually I find typescript's naming of Union and Intersection types very confusing... I haven't yet found any good explanation of why they are named like that :c

[nyfarn]

@paseaf You can think of types as sets of values. The type boolean is the set consisting of the values true and false. The literal type "foo" is the set that only contains that string. Now the union type boolean | "foo" is exactly the union of those two previous sets, a set that consists of those three values. Similarly, boolean & "foo" would be the intersection, the empty set in this case, called never in TS.

Now if you talk about how you can use those types then you get the opposite result. The properties that you can access on a union type is the intersection of the properties of the individual types. So boolean | "foo" has a toString method because both booleans and strings have it. And the properties that you can access on an intersection type is the union of the properties of the individual types. I'm guessing this is what makes these names confusing.

[paseaf]

The properties that you can access on a union type is the intersection of the properties of the individual types.

@nyfarn That's exactly what I was missing! Thank you so much!

I just realized it's another way to think of things. The Union and Intersection are operating on properties of the involved types, and the result are the properties of the result types. This post has also helped me after reading it for a few times.