Configuration

TypeScript

Update the following options in your tsconfig.json (highly recommended):

{
  "compilerOptions": {
    …
    "strict": true,
    "strictNullChecks": true,
    "noUncheckedIndexedAccess": true
  }
}

Other options you may find useful:

{
  "compilerOptions": {
    …
    "noImplicitAny": true,
    "allowUnreachableCode": false,
    "allowUnusedLabels": false,
    "noFallthroughCasesInSwitch": true,
    "noImplicitReturns": true,
    "noUnusedLocals": true,
    "noUnusedParameters": true
  }
}

ESLint

You may also want to add eslint-plugin-functional to your ESLint config. TS Belt returns immutable data, so enabling the functional/prefer-readonly-type rule is recommended.

{
  "plugins": ["functional"],
  "rules": {
    "functional/prefer-readonly-type": "error"
  }
}

Immutable vs Mutable

ts-belt supports immutable arrays by default since it follows the functional programming paradigm. However, starting from v3.11.0 it also gives you the possibility to control whether to use immutable or mutable arrays.

Therefore, if you want to use mutable arrays by default, add global.d.ts in your project and add the following:

declare namespace Belt {
  type UseMutableArrays = 1
}

You can also use F.toMutable (v3.11.0) if you want to quickly coerce a mutable type:

// let's assume that the `numbers` type is `readonly number[]`
const xs = F.toMutable(number) // now `xs` is `number[]`