[TS] Typescript compatibility

[agam]

While there are several versions that are Javascript-compatible, the "pure Typescript" version fails to type check.

• It is possible to use specific versions, e.g. @apache-arrow/es2015-umd.

• It is also possible to use the "umbrella" import apache-arrow.

• However, the @apache-arrow/ts import fails to type check with tsc.

A sample of errors from one file:

../../node_modules/@apache-arrow/ts/schema.ts:46:49 - error TS2345: Argument of type '(Field<T[keyof T]> | undefined)[]' is not assignable to parameter of type 'Field<any>[]'.
  Type 'Field<T[keyof T]> | undefined' is not assignable to type 'Field<any>'.
    Type 'undefined' is not assignable to type 'Field<any>'.

46         return new Schema<{ [key: string]: K }>(columnIndices.map((i) => this.fields[i]).filter(Boolean), this.metadata);
                                                   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

../../node_modules/@apache-arrow/ts/schema.ts:64:58 - error TS2532: Object is possibly 'undefined'.

64                 metadata: mergeMaps(mergeMaps(new Map(), curFields[i].metadata), f2.metadata)
                                                            ~~~~~~~~~~~~

../../node_modules/@apache-arrow/ts/schema.ts:129:22 - error TS2532: Object is possibly 'undefined'.

129         const type = field.type;
                         ~~~~~

(Is there any plan to have the typescript code eventually type-check with tsc ?)

[benmosher]

I can't even import from @apache-arrow/ts in version 7.0.0 because of the .js paths. I made a comment in the commit that added them. Not sure if I'm doing something wrong.

Notably, apache-arrow@7.0.0 gives me all the TS integration I expect so not sure if I even should have tried to import the pure @apache-arrow/ts package anyway.

[hzuo]

The errors you're seeing are due to the fact that your tsconfig is different than the one used by this project.

It looks like your tsconfig has noUncheckedIndexedAccess turned on, which adds a | undefined to every index access.

One way to fix this is to have a tsconfig that is strictly looser than the one used in this repo.

However, almost always that isn't the right solution - you don't in fact want your tsc to compile the TypeScript of your dependencies. Rather your dependencies should publish pre-compiled *.js and *.d.ts files and your tsc should leave them untouched (other than checking that your code is compatible with the *.d.ts declarations).

That's exactly what apache-arrow@7.0.0, @apache-arrow/es2015-esm@7.0.0, etc. already do, so you should use those! @apache-arrow/ts should probably not be published.