Mastering TypeScript 3 - Third Edition

Promise syntax

A promise is an object that is created by passing in a function that accepts two callbacks. The first callback is used to indicate a successful response, and the second callback is used to indicate an error response. Consider the following function definition:

function fnDelayedPromise ( 
    resolve: () => void,  
    reject : () => void)  
    { 
        function afterTimeout() { 
             resolve(); 
        } 
         
        setTimeout( afterTimeout, 2000); 
    } 

Here, we have defined a function named fnDelayedPromise that takes two functions as arguments. These functions are named resolve and reject, and they both return a void. Within the body of the fnDelayedPromise function, we are again calling setTimeout (on the last line of the function) to wait for 2 seconds before calling the ...