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[MUSIC]

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Hi, everyone.

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I'm Alena,
one of the teachers here at Treehouse.

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In this course I wanna talk
to you about something that

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applies to nearly every modern
programming language, REST APIs.

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APIs are one of the most commonly used
interfaces for sharing information across

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both internal products and third party
data sources, such as Twitter and Google.

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Whether you're building or

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consuming an API,
understanding the fundamentals will give

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you a strong foundation before getting
started with language specific tools.

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This course will cover terminology and
structure of API communication, and

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show you examples of this communication
using Postman, a common tool for

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testing API communications.

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REST is really just another later on top
of HTTP, the hyper text transfer protocol,

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which is the foundation for
all communication on the Internet.

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You'll get the most out of this course
if you understand the basics of HTTP.

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You can always review our course
on HTTP before you get started, or

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anytime you'd like clarification.

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Look for a link in the teacher's notes.

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When you build a website or app,
you´re building a user interface for

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your app's logic and data model.

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The point of an API though, is not to
create a traditional user interface, but

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to provide a programmatic interface.

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A code UI, if you will,
to that same logic and data model.

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The major difference is that
the burden of creating the interface

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is on the users of the API and
not the creator.

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Before we talk about REST,

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let's talk about the other
funny word in our title, API.

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API stands for
Application Programming Interface,

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which is a pretty jargony way of talking
about code that makes it easier for

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things outside of an application
to interact with that application.

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Why do we want to provide
gateways like this?

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Well, quite often,
our code is running on one server, or

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even just one kind of server,
like a Java Virtual Machine, and

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we need to talk to it
from somewhere outside.

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Maybe we have a server running for
handling the scores of our game

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from all across the globe and
we want to be able to update those scores,

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whether our players are using a PC,
a mobile device, or a tablet.

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We could write some sort of bridge or
connection layer, but

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we might have to do that for
every new device.

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Building a REST API that works with any
external client, anywhere on the Internet,

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saves us a lot of headaches.

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REST, our other looming acronym, stands
for Representational State Transfer.

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This is yet more tech jargon, but
it'll take a bit more time to explain.

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The web is, by design, stateless.

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This means that every request that you
make to a website is like meeting that

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site for the first time.

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Imagine if your friends were like this.

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You'd have to introduce yourself each
time you spoke in a conversation.

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REST doesn't write this.

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It puts all of the work of
remembering state on the client,

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which is your computer program.

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After each request,
the server forgets your client entirely.

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In fact, you might not even be
talking to the same server each time.

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Your client though, can, and will hold on,
to whatever state information it needs,

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like authentication keys or
previous endpoints.

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Wait, that's a new word.

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Let's talk more about end
points in the next video.