Theo's Typesafe Cult•2y ago

How do I coerce this function to accept multiple types then conditionally change the output?

Using traditional overloading approach doesn't seem to work as expected. Union types on parameters does not resolve the output type properly:

const convertInfluenceType = (type: InfluenceTypeEnum | number)
// Outputs InfluenceTypeEnum | 1 | 4 | 7

const convertInfluenceType = (type: InfluenceTypeEnum | number)
// Outputs InfluenceTypeEnum | 1 | 4 | 7

Error:

Type '(type: number | InfluenceTypeEnum) => InfluenceTypeEnum | 1 | 4 | 7' is not assignable to type 'ConvertFn'.
  Type '(type: number | InfluenceTypeEnum) => InfluenceTypeEnum | 1 | 4 | 7' is not assignable to type '(type: number) => InfluenceTypeEnum'.
    Type 'InfluenceTypeEnum | 1 | 4 | 7' is not assignable to type 'InfluenceTypeEnum'.
      Type '1' is not assignable to type 'InfluenceTypeEnum'.

Type '(type: number | InfluenceTypeEnum) => InfluenceTypeEnum | 1 | 4 | 7' is not assignable to type 'ConvertFn'.
  Type '(type: number | InfluenceTypeEnum) => InfluenceTypeEnum | 1 | 4 | 7' is not assignable to type '(type: number) => InfluenceTypeEnum'.
    Type 'InfluenceTypeEnum | 1 | 4 | 7' is not assignable to type 'InfluenceTypeEnum'.
      Type '1' is not assignable to type 'InfluenceTypeEnum'.