Ok, let’s talk about
KoaJs. Why?
Well, it’s new and shiny. But that’s not it.
And it’s tiny and stays out of your way. But that’s not it.
It’s created by the awesome
crew behind
ExpressJs (and others). But that’s not it.
It teaches me about new things. And really strange things. Like
generators for example. But that’s not it.
No.
The
Reason
I
really
wanted
to
get
your
really important fact that we would like to
hold on to in the rest of the text
attention
is
something
different
altogether.
This has
to
Stop.
I’m by no means a seasoned Javascript developer
but I’m already starting to dislike the code callbacks forces me to write. Yeah, I know, there
are ways around it with
promises
and everything, but still have a hard time grasping that. Sorry. I hope
there’s another way ^^
I mean; “getUserFromDatabase()”…
what would you expect that to return? An user? Or a promise maybe? I
wouldn’t think so either. I want the user, if you could please…
That said, I love the way that Node puts scalability first. To do that
we have (?) to provide promises and callbacks. Or do we?
What if I said that you didn’t? You could do without callbacks and
promises altogether. What if
KoaJs…?
Writing the code like you understand it.
Now, mind you (and me) well, that this is cutting edge stuff. This is
using proposed features of the next version of Javascript. So it’s still
a bit rough around the edges. But the promise (pun intended) of getting
a nicer structure and get rid of the callbacks makes me tolerant.
I hope to be able to explain to you how it works and get your journey to
be a bit smoother than mine. In this post I just want us to get up and
running. And that’s not as easy as one would first think…. The goal
today is to be able to run a few examples.
Getting started
There’s two parts to installing Koa; updating Node to the required
version and installing Koa.
Most blog posts about Koa (and the KoaJs.com site itself) says something
like: “Koa needs Node 0.11.9 or higher to run”. “Well thank you. I’m a
newbie at these things. How do I do that then?” was something i asked
myself.
Btw, this require that you have Node installed. If not you can go to
www.nodejs.org and hit the Install button to
get it on your system.
Update Node, the safe way
The first thing I thought was “If I’ll update my Node installation to
something bleeding edge… will the rest of my things work?” Luckily
there’s a little nice tool that helps you with this. It’s called
Node Version
Manager, or nvm for short.
Not only does this tool make it super easy to install new versions of
Node but also you can easily switch between versions, when you need to
“head back to safety”.
Install Node Version Manager
Installing the nvm by running the following command:
sudo
curl https://raw.github.com/creationix/nvm/master/install.sh |
sh
This command pulls in the install.sh script form that url and executes
it. There’s a number of things going on in the script, setting
path-variables etc. When it’s done, and you have restarted the terminal
(?), you will have a couple of new commands at your disposal. You can
see them all by running “nvm
help”.
If that doesn’t work out for you make sure to read the ReadMe (hmmm
wonder why it’s called that :)) on the
nvm github
site. There’s a couple of manual tricks, adding stuff to the bashrc
(whatever that is) for example, that I needed to do to get this to work
on one of my vm’s.
Installing a version of Node
One of those new commands is “nvm install”. Let’s do that now to get a
version that is needed for Koa (at least 0.11.9):
nvm
install 0.11.9
You can see the versions available for download by “nvm
ls-remote”, so you can pick a later version when this post is out
of date. Which in Javascript land is in about 20 minutes…
Using a version
We have now only installed a version and it's also set as our current
version. If you go "
nvm
current" you will see the version you are currently using. Or
have "loaded" if you want to.
If you want to use another version you just go "
nvm use
0.10.8" for example. But, Marcus, how can I see which versions of
Node I have installed then, you ask. Funny that you should ask that, he
responded with light laughter. That's simple
> nvm
> ls
Will list the versions you have installed on your system, as well as
mark the one you are running in green. For the rest of this article make
sure that you have run "nvm use
0.11.9" or higher than that.
### Installing Koa
That was the first part, preparing the way for installing Koa.
Thankfully that is much easier. It's really just a normal
npm
package. Let's be good programmers and set this up properly. Create
a new directory and call it KoaFirstStumblingSteps
or something that describes what we are doing. cd into that directory
and then run "npm init"
to get some nice
wizardry help to create the package.json.
When that is done you can go "npm install koa
--save" to install koa in your directory and save the reference
in the package.json.
Here's those steps in sequence:
- mkdir KoaFirstStumblingSteps
- cd KoaFirstStumblingSteps
- npm
init
- \[a lot of questions that are quick to answer... Enter works for
most of them. 0.45 sec to completion is my record\]
- npm
install koa --save
Alright. You should have seen quite a lot of things coming down with
that last command. I'll come back to that, but it has to do with Koa
believing very hard in modularity and composability. Or "it's made from
a lot of small Legos (c)", if you're a parent like me.
We have set ourselves up for some Koa code. Let's dive right in. Create
a firstKoaSite.js file and ~~type the following~~ copy (who am I
kidding?) the following code into it:
I wanted to do something just a little more than a hello world and yet
not complicated at all. For this we need the "koa-route" middleware. No,
it's not included in Koa. Yes, middleware in Koa are tiny, so you end up
including many of them.
Install with "npm
install koa-route --save" and we are ready to run.
It's pretty self-explanatory and short and sweet. Just like we like
it:
- Line 1,2 requires the things we need
- Line 3 creates the actual Koa app
- On line 8-9 we set up a couple of routes (via koa-route) using the
app.use()
- The routes calls out to a couple of functions. Note anything
strange? Yes, the asterisk should be there. It's a generator
function the
next post is about that.
- Finally on line 24 we fire the application up and shows how to call
it
### Running your first Koa site
Running a Koa site is just starting it as normal with "node
firstKoaSite.js" except it isn't... You need to add a flag to use
the "harmony"-features of Node. This is using some of the cutting edge
features of Javascript, normally not included. Like generators for
example, which Koa is built around.
The complete command to run our first little site is in other words:
> node
> --harmony firstKoaSite.js
Exactly! I don't want to type that every time either... Better enter it
into the package.json, under scripts, and use
nodemon so that we don't need to restart our server
manually on every change we make.
This is the scripts-node of my package.json.
"scripts":
{
"start":
"node_modules/nodemon/bin/nodemon.js --harmony
firstKoaSite.js"
}
Which lets me start my site like this:
> npm
> start
Ahhh! Much better. And the site runs nice too. Looks like crap but
that's normal and expected for my sites. But with the proper indata
(<http://localhost:3000/whosThere/World>) you can get it to be a Hello
World application
> Ah, it is
> you! My old friend!
> Hello World
### Conclusion
This ends this first little post on Koa. I'm planning to write another
one to try to explain yield and generators. If for none other so for
myself. And then use more of Koa's features in some more sites. The goal
of this post was merely to get us off the ground.
During this exploration I have had great use of the following resources:
- <http://tamas.io/replacing-express-with-koa/> - that showed me Node
Version Manager. Thank you!
- <http://weblogs.asp.net/shijuvarghese/archive/2014/01/12/a-simple-crud-demo-with-koa-js.aspx>
- And of course
http://www.koajs.com
and especially the exemplary documentation.
My code is in those gists listed above or here in a repo.
I like Koa Js. I've written a couple of post about it. Here they will be
when they are published:
- Let's talk about Koa for a while, shall we? (this post)
- Let's talk about yield and generators, shall we?
- Marcus Node Bits: Let's flex Koa Js, shall we?
