Tricks I wish I knew when I learned TypeScript

Post by ketzo » Tue, Oct 12, 2021, 4:52 PM UTC

skywal_l wrote: post #58

mithusingh32 wrote: post #56

Earlier quoted context omitted.

Wow, thanks for this. I wasn't even aware of these. I'm surprised I rarely see these in courses/tutorial. These should be like day 1 material.

Typescript is actually a great language. And with those utility types, you can do pretty fun stuff like, for example, you want to mutate a type so that some fields become mandatory: type Ensure = T & { [U in keyof Pick ]-?: T[U] }; class A { foo?: number; bar?: number; baz?: number; } type MandatoryFields = "foo" | "baz"; type B = Ensure ; const b: B = { foo: 42 }; Here, ts will complain that b is missing baz.

Post by ketzo » Tue, Oct 12, 2021, 4:55 PM UTC

nosianu wrote: post #61

BoorishBears wrote: post #51

Earlier quoted context omitted.

That example disappointed me a little. It was an easy catch because I was told there's an issue, but I'm surprised const arrays don't at least have a warning there. Or even default to having readonly-like behavior

Which "const" do you mean? The one in front of a variable declaration cannot make the array itself constant. That's because that "const" only refers to that variable itself, which is just a pointer (except for the primitive types). The variable declaration "const" means this variable cannot be changed to point to a different object. It says nothing about the thing it points to and that is how that keyword was designe…

Post by jgwil2 » Tue, Oct 12, 2021, 4:58 PM UTC

skywal_l wrote: post #101

yulaow wrote: post #90

Earlier quoted context omitted.

This seems extremely hard to read for me, I would have an hard time trying to understand what it does if I found it in any source code

type Ensure I define a type called Ensure This type takes two type parameters, one called T and the other K which will consist of Keys belonging to the type T (in our case, "foo", "bar" or "baz"). = T & This new type (called Ensure) will be equal to the union of two types: One will be T and the other will be: { [U in keyof Pick ] A new type which keys will be picked among the key listed in K -? To which we will remov…

Post by irrational » Tue, Oct 12, 2021, 5:11 PM UTC

Post by spicybright » Tue, Oct 12, 2021, 5:22 PM UTC

bmn__ wrote: post #97

spicybright wrote: post #94

I'm going to be one of those people, but multiple "=" rendering as a large double line is really ugly.

You don't have to suffer (subjectively) bad typography. Cascading style sheets were designed with the ability to override author styles with user styles, your Web browser has settings for this.