Use TypeScript to trigger a compile error when BigNumber.toString is used?

Question

Is it possible to use TypeScript to trigger a compile-time error if BigNumber.toString is called?

Specifically, my application has experienced bugs because BigNumber.toString() will express sufficiently large and sufficiently small numbers in scientific notation:

> x = new BigNumber('0.00000000001')
> x.toString()
'1e-10'
> x.toFixed()
'0.00000000001'

I've tried overriding the type:

import {BigNumber} from "bignumber.js";

declare module "bignumber.js" {
  interface BigNumber {
    toString: never
    someOtherThing: number
  }
}

But this doesn't seem to work (and the someOtherThing field is added, so I know the type definitions are being loaded)

How can I trigger a compile error if BigNumber.toString is used?

(also, note: I have set BigNumber.config({ EXPONENTIAL_AT: 1e+9 }) and overloaded BigNumber.toString so it issues a warning, but it would be nice to have the added compile error)

Answer 1

Is it possible to use TypeScript to trigger a compile-time error if BigNumber.toString is called

Few options

Create a custom linter rule

Docs on tslint : https://palantir.github.io/tslint/develop/custom-rules/ You custom rule would be type checking rule : https://palantir.github.io/tslint/usage/type-checking/

And change toString invocations on BigNumber to be an error.

Edit the types on install

Remove the toString method from BigNumber by editing the installed .d.ts and commit it using PatchPackage : https://github.com/ds300/patch-package

Create a wrapper

Alternatively create a wrapper around BigNumber that doesn't expose anything you consider dangerous to your fellow developers 🌹

Thoughts

I would personally use patch package as its the easier route. If you are doing a lot of financial work with the library then consider a wrapper for your use case.