To have a better understanding of the differences between Promises and traditional callbacks, consider an asynchronous task like this:
function process(callback) {
stepOne((error, resultOne) => {
if (error) {
callback(error);
return;
}
stepTwo(resultOne, (error, resultTwo) => {
if (error) {
callback(error);
return;
}
callback(undefined, resultTwo + 1);
});
});
}
If we write preceding above in Promise style, it would be as follows:
function process() {
return stepOne()
.then(result => stepTwo(result))
.then(result => result + 1);
}
As in the preceding example, Promise makes it easy and natural to write asynchronous operations with a flat chain instead of nested callbacks. But the most exciting thing about Promise might be the benefits it...