Sometimes, you want to optionally wait for a promise before performing some synchronous code. The most obvious solution unfortunately leads to some duplication:
function onExit() {
if (hasChanges) {
showConfirmationModal()
.then(() => goToHomePage());
} else {
goToHomePage();
}
}
The more complicated a flow gets, the more unwieldy it becomes. A good way of dealing with this is by introducing what I sometimes call a maybePromise:
function onExit() {
const maybeConfirmExit = hasChanges ? showConfirmationModal() : Promise.resolve();
maybeConfirmExit.then(() => goToHomePage());
}
This can really simplify more complicated flows which include more than one optional gate:
function onExit() {
const maybeConfirmExit = hasChanges ? showConfirmationModal() : Promise.resolve();
const maybeNotifySessionEnded = () => otherSessions.length ? notifySessionEnded() : Promise.resolve();
maybeConfirmExit
.then(maybeNotifySessionEnded) // !important, maybeNotifySessionEnded is an arrow function
.then(() => goToHomePage());
}
This works really well in Angular 1 too, where you can use $q.when() instead of the ES6 Promise.resolve()