Typescript errors in bignumber.ts wrapper file

[dnlaviv]

Hey all,

I'm using ethers@^5.5.1 in my next-js web application.

As part of the production build process, the compiler is running typescript checks on all node_modules libraries that were imported into the project.

I'm getting this error in bignumber.ts file:

Failed to compile.

./node_modules/@ethersproject/bignumber/src.ts/bignumber.ts:11:17
Type error: Could not find a declaration file for module 'bn.js'. '/Users/daniel/WebstormProjects/kylender/node_modules/bn.js/lib/bn.js' implicitly has an 'any' type.
  Try `npm i --save-dev @types/bn.js` if it exists or add a new declaration (.d.ts) file containing `declare module 'bn.js';`

As the error message suggested, I went ahead and installed @types/bn.js@5.1.0 npm package.
This solved the first TS error, but introduced a couple of more:

Failed to compile.

./node_modules/@ethersproject/bignumber/src.ts/bignumber.ts:190:9
Type error: Type 'null' is not assignable to type 'number'.

  188 |             throwFault("overflow", "toNumber", this.toString());
  189 |         }
> 190 |         return null;
      |         ^
  191 |     }
  192 | 
  193 |     toBigInt(): bigint {
error Command failed with exit code 1.

I jumped into the file and saw this warning, as well as some other ones that might be worth looking at.
I added screenshots from my IDE with the description and line number:

When I set the compiler to skip all typescript checks, the application works as expected.
I hope it's the right place for me to post this issue, it's not a bug, but it blocks the deployment process for typescript developers who uses nextjs / webpack 5.

It's also worth mentioning that the same errors were in 'ethers@^5.4.6'.

Prior to creating this issue, I used the search terms: "typescript", "bignumber" "bn.js" "nextjs".

Thanks for you guys's help!

I love using ethers, it's way better than web3.js ;)

[ricmoo]

It's not usually a good a idea to type check dependencies within the node_modules/ and is something not supported in v5. Due to the large number and breadth of environments, platforms and versions that ethers v5 is compatible with, it is nearly impossible to make everything stable in this fashion.

A lot of this goes away in v6, which I'm working on now and hoping in another couple weeks to get a beta version out for. In v6, everything is targeted for ESM, uses strict typing and all dependencies are TypeScript, so there are none of these weird commonjs bridging issues.

So this will not be changed in v5 as I'm trying to focus my time on getting v6 out. For now the best solution is to not type check dependencies.

Hope that makes sense. :)

[ricmoo]

(oh, thanks for your comments btw, glad you like it ;) I'll move this to discussions, in case others have more to say too)