Now that you've seen promises in action in your own code,

I'll show you some examples of promises in real world scenarios.

Sequelize is a Node.js ORM, a way for Node.js to talk to a database.

Let's look at the example code here.

Sequelize wants to synchronize the schema we've defined here.

Once that's done, it wants to create a user.

Once the new user has been created, after an asynchronous call to the database.

The promised value of the new user

is passed along to the next promise to resolve.

Remember, you want to use promises when asynchronous calls are happening.

And not to block the system where the Node.js application is running.

You'll find that the ORM model layer in many JavaScript frameworks

has this promise pattern.

The same goes for bookshelf.

Once the results are fetched, there's a then and a catch of a promise.

You may have heard of Ember j.s..

It's a front end framework for creating user interfaces.

Without going into too much detail,

Ember.js uses promises to handle asynchronous routing.

To perform asynchronous operations and handle code in a more human readable way.

And then there's the $q service in Angular,

which is used to wrap anonymous functions in a promise.

In other words, Angular has promises built in.

The $q function is basically a promise constructor requiring resolve and

reject handlers.

JQuery has a version of promises called deferred objects.

Take a look at this example code.

JQuery is performing an AJAX call, it returns a deferred object.

In other words, jQuery's version of a promise, that you can use the then method

to handle the resolution and the rejection of the promise.

Finally, new browser APIs are now using promises.

For example, fetch, which is a modern way to perform AJAX requests,

returns a promise.

In this example, the flowers image is downloaded asynchronously.

Once it's downloaded, the raw data is returned.

This promise is resolved and

then converted into a data URL for the selected image.

Then there's the Battery Status API.

This is used to get the battery charging information for laptops and mobile phones.

If you know the battery is at a certain percentage,

you may want your application to save the information or warn the user.

There are many more instances of promises in the wild.

And now you know how to use them.