Mastering TypeScript 3 - Third Edition

Callback versus promise syntax

By way of a comparison of the two techniques we have discussed, let's take a look at a simplified version of the callback versus the promise syntax, as follows:

Our standard callback mechanism is as follows:

function standardCallback() { 
    function afterCallbackSuccess() { 
        // execute this code 
    } 
    function afterCallbackError() { 
        // execute on error 
    } 
    // invoke async function 
    invokeAsync(afterCallbackSuccess, afterCallbackError); 
}

And our promise syntax is as follows:

function usingPromises() { 
    delayedPromise().then( 
        () => { 
            // execute on success 
        } 
    ).catch ( 
        () => { 
            // execute on error 
        } 
    ); 
} 

As we can see, using promises introduces a fluent syntax for handling asynchronous programming.