Allow defining static index signature

[iby]

class Foo {
    [key: string]: any;
    static BAR:string = 'bar';
    static BAZ:string = 'baz';
}

console.log(Foo['BAR']);
console.log(Foo['B' + 'A' + 'Z']);
console.log(Foo['qux']);

I get the following errors with this:

tst.ts(8,13): error TS7017: Index signature of object type implicitly has an 'any' type.
tst.ts(9,13): error TS7017: Index signature of object type implicitly has an 'any' type.

I've read in the gitter archives that this should be working. Should it? How can I get a static property value using a dynamic key?

[iby]

Figured that I can access the value of a static property using the following notation. Is that error expected though? Is that because [key: string]: any for instances only?

console.log((<any>Foo)['B' + 'A' + 'Z']);
console.log((<any>Foo)['qux']);

[RyanCavanaugh]

You're correct -- the declared index signature only applies to the instance side of the class, not the constructor function itself.

Presumably we'd allow you to fix this without a type assertion by writing static [key: string]: any in the class declaration but that's currently disallowed. I don't see any obvious reason why it couldn't be allowed, though.

[iby]

Frankly static [key: string]: any was the first instinct. Tried it. Didn't work. I think it would be a very natural thing to have.

[RyanCavanaugh]

It makes sense from purely a code perspective... but what are you doing, exactly? When designing this feature we basically said "Do we ever need static index signatures?" and thought about it a bunch and came up with no user scenarios, so it'd be great to understand what kind of pattern you're writing. Thanks!

[iby]

I have a class which acts like enum and holds a bunch of constants. Though there are string enums, this is more appropriate & convenient for my case. And I need to check if the constant is there or not, which doesn't work nicely with Foo['…'] syntax. The example above shows that in full.

[RyanCavanaugh]

Accepting PRs. This should be a fairly easy change for someone familiar with the compiler, just checking for some flags during type construction.

[markspolakovs]

Has there been any progress on this in the past year? I'm running into this in a project, and it's blocking me, but I am not "familiar with the compiler", so I cannot make the fix myself.

[nikis05]

@RyanCavanaugh Obviously need this feature. My usecase:
• I write a framework that offers a class that is to be extended by the user;
• The extended class can have additional methods, both instance (no problem with this) and static;
• The framework needs to operate on these methods added by the user, aka

let method = isMethodStatic ? ExtendedClass[methodName] : new ExtendedClass(someData)[methodName]

Writing ExtendedClass[methodName] is currently impossible and there is no elegant workaround.

[kitsonk]

Accepting PRs means that the core team do not have the time to address this and it is open to the community to solve.

[Kingwl]

friendly ping @ianbytchek @nikis05 @markspolakovs

I have a pr for this one.
You could take a preview here(if you still need that).

[hengkx]

same problem.

[DanielRosenwasser]

Thanks @Kingwl!