How to return a proper Promise with TypeScript

Question

So I am learning Angular 2 with typescript.

I am reaching a point to write a mocking service which (I believe) should return a Promise if the service get the Object Successfully and Return an Error if anything happens.

I have tried following code but looks like it is not a write syntax for typescript.

Updated the CODE:

saveMyClass(updatedMyClass: MyClass){         //saving MyClass using http service         //return the saved MyClass or error         var savedMyClass : MyClass = someLogicThatReturnsTheSavedObject(updatedMyClass);         if(isSomeCondition)             return Promise.reject(new Error('No reason but to reject'));         else             return new Promise<MyClass>(resolve => {setTimeout( ()=>resolve(savedMyClass),1500  )}  );     } 

But to my surprise, the typescript complained that "No best common type exists among return expressions".

What should be the right code? So that I could use on my component to consume if proper MyClass is returned and reflect error if any exists from service.

Thanks

Answer 1

It is considered a good practice to embed the whole function body inside the Promise constructor, so should any error happen, it would be converted to a rejection. In this case it solves your problem too I believe.

saveMyClass(updatedMyClass: MyClass) {     return new Promise<Package>((resolve, reject) => {         //saving MyClass using http service         //return the saved MyClass or error         var savedPackage : Package = updatedPackage;         if (isSomeCondition) {             throw new Error('No reason but to reject');         }          setTimeout( () => {             resolve(savedPackage);         }, 1500);     }); }