CODEWITHSUNDEEP
typescript
u936293
u936293

Reputation: 16264

Return type of resolve parameter is inferred as an object?

The following won't compile:

function P() {
   return new Promise((resolve, reject) => {
      const stringValue:string = "...explicit string...";
      resolve(stringValue);
   });
}

async function f() {
  let s:string = "";
  await P().then((res) => { s = res; });
}

The error is at the statement s = res:

[ts] Type '{}' is not assignable to type 'string'.

Why is this happening?

Upvotes: 0

Views: 50

Answers (1)

Akash Kava
Akash Kava

Reputation: 39946

You have to explicitly specify return type.

function P(): Promise<string> {
   return new Promise((resolve, reject) => {
      const stringValue:string = "...explicit string...";
      resolve(stringValue);
   });
}

async function f() {
  let s:string = "";
  await P().then((res) => { s = res; });
}

TypeScript assumes return type of P is Promise<{}> when you do not specify return type. You can check it at https://www.typescriptlang.org/play/index.html , type your code on left side and put mouse on P().then( , you will see that typescript assumes return type as Promise<{}>.

Upvotes: 1

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