Compiler fails to recognize Type Guard

I seem to be experiencing an issue with the Typescript compiler in this particular case, despite my belief that there shouldn't be any problem

type Car = {
  isOn: boolean
  name: string
}


function doSomething(key: keyof Car, value: string | boolean) {
  const car: Car = {
    isOn: false,
    name: "myCar",
  }
  if (typeof car[key] === typeof value) {
    car[key] = value
  }
}

Error Message:

"TS2322: Type 'string | boolean' is not assignable to type 'never'.   Type 'string' is not assignable to type 'never'."

Do you see where I might have gone wrong?

Answer №1

It is important to template the type of the result in order for it to be inferred correctly:

function performAction<K extends keyof Vehicle>(key: K, value: Vehicle[K]) {
   // ...
}

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