Theo's Typesafe Cult•14mo ago

Function overloads with more than 1 parameter

Im trying to overload a function that the first two parameters are string and are not optional, the first parameter should be an union type of strings and the second parameter should also be a union type of strings but these should depende on the first parameter. For example, we have the next function

  function callOutsideFunction(module: string, method: string): unknown

  function callOutsideFunction(module: string, method: string): unknown

where the module can be climate and date and when i pass any of those have the correct possible methods. I tried overloading the function like this:

function callOutsideFunction(module: 'climate', method: 'climateMethod 1' | 'climateMethod2'): unknown
function callOutsideFunction(module: 'date', method: 'dateMethod 1' | 'dateMethod2'): unknown

function callOutsideFunction(module: 'climate', method: 'climateMethod 1' | 'climateMethod2'): unknown
function callOutsideFunction(module: 'date', method: 'dateMethod 1' | 'dateMethod2'): unknown

but I end up having a union type of all the methods even though I pass certain module as a parameter. Is there any way of fix this?

1 Reply

whatplan•14mo ago

object with discriminated union

type Foo =
  | {
      module: 'climate';
      method: 'climateMethod1' | 'climateMethod2';
    }
  | {
      module: 'date';
      method: 'dateMethod1' | 'dateMethod2';
    };

function callOutsideFunction({ module, method }: Foo) {
  if (module === 'climate') {
    //HOVER METHOD = 'climateMethod1' | 'climateMethod2'
    method
  } else {
    //HOVER METHOD = 'dateMethod1' | 'dateMethod2'
    method
  }
}

type Foo =
  | {
      module: 'climate';
      method: 'climateMethod1' | 'climateMethod2';
    }
  | {
      module: 'date';
      method: 'dateMethod1' | 'dateMethod2';
    };

function callOutsideFunction({ module, method }: Foo) {
  if (module === 'climate') {
    //HOVER METHOD = 'climateMethod1' | 'climateMethod2'
    method
  } else {
    //HOVER METHOD = 'dateMethod1' | 'dateMethod2'
    method
  }
}

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Function overloads with more than 1 parameter