Mastering TypeScript 3 - Third Edition

Returning values from promises

So far, we have defined all of our promise objects as Promise<void>. The void in this case indicates that our promises will not return any values. If we use Promise<string>, this indicates that our promises will return string values. Let's take a look at how to return values from promises, as follows:

function delayedPromiseWithParam() : Promise<string> { 
    return new Promise<string>(  
        ( 
            resolve: (str: string) => void,  
            reject: (str:string ) => void  
        ) => { 
             
            function afterWait() { 
                resolve("resolved_within_promise"); 
            } 
            setTimeout( afterWait , 2000 ); 
        }  
    ); 
}

Here, we have a function named delayedPromiseWithParam that constructs and returns our promise object as usual. Note, however, that the definition of both the ...