type Answer = { error: false; status: boolean } | { error: true; description: string };

   async has_READ_EXTERNAL_STORAGEv1(): Promise<Answer> {
     return await this.androidPermissions
      .checkPermission(this.permission.READ_EXTERNAL_STORAGE)
      //.then((current) => ({ error: false, status: current.hasPermission})) <--ERROR
      //.then((current) => ({ error: false as const, status: current.hasPermission})) <--NO ERROR
      .catch((error) => ({ error: true, description: error.message as string}));
   }

ERROR

Type '{ error: boolean; status: boolean; } | { error: true; description: string; }' 
is not assignable to type 'Answer'.
Type '{ error: boolean; status: boolean; }' is not assignable to type 'Answer'.
Type '{ error: boolean; status: boolean; }' is not assignable to type '{ error: false; status: boolean; }'.
Types of property 'error' are incompatible.
Type 'boolean' is not assignable to type 'false'.ts(2322)

p.s.: if I return it as 'as const' I don't get any error, however, when I use the function it does not detect the status property.

2nd ERROR

Property 'status' does not exist on type 'Answer'.
Property 'status' does not exist on type '{ error: true; description: string; }'

First Edit

async has_READ_EXTERNAL_STORAGEv1(): Promise<Answer> {
  return await this.androidPermissions
    .checkPermission(this.permission.READ_EXTERNAL_STORAGE)
    .then((current) => ({ error: false, status: current.hasPermission} as Answer))
    .catch((error) => ({ error: true, description: error.message as string} as Answer));
}

p.s.: when I use the function, it keeps telling me that the status property does not exist.

2nd Edit

await this.has_READ_EXTERNAL_STORAGEv1().then(answer => {
  if (!answer.error) {
    console.log(answer.status); // <--Error
    // when I use the function, it keeps telling me that the status property does not exist.
  } else {
    console.log(answer.description);
  }
});

CodePudding user response：

!answer.error seems to be too vague for the compiler to infer the type.

answer.error === false works as you expect.

await this.has_READ_EXTERNAL_STORAGEv1().then(answer => {
  if (answer.error === false) {
    console.log(answer.status);
  } else {
    console.log(answer.description);
  }
});

Stackblitz: https://stackblitz.com/edit/typescript-yatio3?file=index.ts