TS2412: exactOptionalPropertyTypes property assignment - in CI

By Kaveh Alemi·Latchkey

With exactOptionalPropertyTypes on, directly assigning undefined to an optional property fails unless the property type includes undefined.

What this error means

Type-checking fails with TS2412 at a property assignment that sets an optional field to undefined.

src/config.ts(9,3): error TS2412: Type 'undefined' is not assignable to type 'string' with 'exactOptionalPropertyTypes: true'.

Common causes

How to fix it

Include undefined in the property type

1. Declare the optional property as type | undefined where appropriate

interface Config { region?: string | undefined }

Skip the assignment when there is no value

1. Conditionally assign only when a value exists, leaving the key absent otherwise

if (region) config.region = region

How to prevent it

• Treat optional and undefinable as distinct under exactOptionalPropertyTypes and only assign present values.

Frequently asked questions

Related guides

References

• Node.js documentation
• npm CLI documentation
• GitHub Actions documentation