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Jester: JavaScriptian REST

Eric Mill

Jester is our implementation of REST, in JavaScript. It provides (nearly) identical syntax to ActiveResource for using REST to find, update, and create data, but from the client side.

Update, 6/16/07: We have released version 1.3 of Jester. You may want to view its release description.

Jester is available from SVN in trunk form, or a 1.1 release form. You can also download a zipped copy of 1.1. Jester is released under the MIT License.

Syntax

All examples below are taken from inside the JavaScript console of Firebug, the best JavaScript development tool you could possibly have.

First, declare a model in Jester by calling model on Base:

>>> Base.model("User")
>>> User
Object _name=User _singular=user _plural=users

This creates a global variable called User. It assumes that the URL prefix it uses to base its HTTP requests from is the current domain and port, and assumes “user” and “users” as single and plural forms to make these URLs. There’s no “people/person” intelligence here, so make sure to override these defaults if you need to, like so:

>>> Base.model("Child", "https://thoughtbot.com", "child", "children")
>>> Child
Object _name=Child _singular=child _plural=children

If you want to capture the model created in a local variable, or simply prefer more traditional JavaScript syntax, you can do:

>>> var Child = new Base("Child", "https://thoughtbot.com", "child", "children")
>>> Child
Object _name=Child _singular=child _plural=children

Find will retrieve a particular instance of your model. Attributes are auto-converted to integer or boolean types if that’s what they are on the server side. The “GET” line is not a return value, just Firebug’s report of activity, but relevant to understanding what’s happening.

>>> eric = User.find(1)
GET http://localhost:3000/users/1.xml
Object _name=User _singular=user _plural=users

>>> eric.attributes
["active", "email", "id", "name"]

>>> eric.id
1
>>> eric.name
"Eric Mill"
>>> eric.active
true

Create takes a hash of attribute values. After calling create, the model will fetch its new ID from the return headers.

>>> floyd = User.create({name: "Floyd Wright", email: "tfwright@thoughtbot.com"})
POST http://localhost:3000/users.xml
Object _name=User _singular=user _plural=users

>>> floyd.id
9

>>> User.find(9).name
GET http://localhost:3000/users/9.xml
"Floyd Wright"

Updating is as simple as changing one of the properties and calling save.

>>> eric = User.find(1)
GET http://localhost:3000/users/1.xml
Object _name=User _singular=user _plural=users

>>> eric.email
"emill@thoughtbot.com"
>>> eric.email = "sandybeach@wintermute.com"
"sandybeach@wintermute.com"

>>> eric.save()
POST http://localhost:3000/users/1.xml
true

>>> User.find(eric.id).email
GET http://localhost:3000/users/1.xml
"sandybeach@wintermute.com"

Sadly, there’s one area where Jester’s syntax can’t match ActiveResource’s perfectly. The method “new” has been renamed to build, due to “new” being an illegal method name in JavaScript up to 1.6. Hopefully this can be updated as the browser landscape evolves. Build was chosen because it is similarly used in ActiveRecord to replace “new” on an association array, where “new” cannot be used.

>>> chad = User.build({email: "cpytel@thoughtbot.com", name: "Chad Pytel"})
Object _name=User _singular=user _plural=users

>>> chad.new_record()
true
>>> chad.save()
POST http://localhost:3000/users.xml
true

>>> chad.id
9
>>> chad.new_record()
false

Error validations are supported. If a model fails to save, save returns false, and the model’s errors property is set with an array of the error messages returned.

>>> jared = User.build({name: "", email: ""})
Object _name=User _singular=user _plural=users

>>> jared.save()
POST http://localhost:3000/users.xml
false

>>> jared.errors
["Name can't be blank", "Email can't be blank"]
>>> jared.valid()
false

>>> jared.name = "Jared Carroll"
"Jared Carroll"
>>> jared.email = "emill@thoughtbot.com"
"emill@thoughtbot.com"

>>> jared.save()
POST http://localhost:3000/users.xml
false

>>> jared.errors
["Email has already been taken"]
>>> jared.email = "jcarroll@thoughtbot.com"
"jcarroll@thoughtbot.com"

>>> jared.save()
POST http://localhost:3000/users.xml
true

Lastly, associations are also supported. If the association data is included in the XML, they’ll be loaded into the returned model as Jester models of their own, using the same assumptions on naming and URL prefix described above. They’re full models, so you can edit and save them as you would the parent. Has_many relationships come back as simple arrays, has_one relationships as a property. In this example, User has_many :posts, and Post belongs_to :user.

>>> eric = User.find(1)
GET http://localhost:3000/users/1.xml
Object _name=User _singular=user _plural=users

>>> eric.posts
[Object _name=Post _singular=post _plural=posts,
  Object _name=Post _singular=post _plural=posts]

>>> eric.posts.first().body
"Today I passed the bar exam. Tomorrow, I make Nancy my wife."
>>> eric.posts.first().body = "Today I *almost* passed the bar exam. The ring
  waits one more day."
"Today I *almost* passed the bar exam. The ring waits one more day."

>>> eric.posts.first().save()
POST http://localhost:3000/posts/1.xml
true

>>> post = Post.find(1)
GET http://localhost:3000/posts/1.xml
Object _name=Post _singular=post _plural=posts

>>> post.body
"Today I *almost* passed the bar exam. The ring waits one more day."
>>> post.user
Object _name=User _singular=user _plural=users
>>> post.user.name
"Eric Mill"

Using Jester

Jester depends on two libraries: Prototype, which comes with Rails and most people are familiar with, and ObjTree, a nice DOM parsing engine for JavaScript. Both of these are packaged along with Jester in its SVN repository, so you don’t have to hunt for them yourself. Just make sure you’re including all three in your test file.

<script type="text/javascript" src="/javascripts/prototype.js"></script>
<script type="text/javascript" src="/javascripts/ObjTree.js"></script>
<script type="text/javascript" src="/javascripts/jester.js"></script>

JavaScript in the browser is limited to requests with in only the same domain as the script is running in, so without iframe hackery, Jester is probably only useful for writing client code in your own apps, to talk to itself. We’re investigating whether Jester can use this hackery to make cross-domain requests, but it’s not clear if this will be feasible.

There are also some basic unit tests included inside Jester’s repository, which run using JsUnit. To run them yourself, from Jester’s repository open the file test/jsunit/testRunner.html in your browser, and choose test/jester_test.html as the test file.

The Server Side

These examples are talking with a Rails application whose controllers were generated with ./script generate scaffold_resource—in other words, the ideal RESTful controllers. It’s very easy to make your controller RESTful. Here’s the source for the User controller I’m using. The lines that deal with returning HTML have been removed, and I have added (:include => :posts) as an argument to to_xml in two places, so associations are included (it’s that easy!).

<script type="text/javascript" src="/javascripts/prototype.js"></script>
<script type="text/javascript" src="/javascripts/ObjTree.js"></script>
<script type="text/javascript" src="/javascripts/jester.js"></script>

An example of the XML produced here, of a User with one Post, at /users/2.xml:

<user>
  <active type="boolean">true</active>
  <email>cpytel@thoughtbot.com</email>
  <id type="integer">2</id>
  <name>Chad Pytel</name>
  <posts>
    <post>
      <title>Life as a Jester</title>
      <body>It's not as hard as Master said it would be.  Today I made 200 dollars.</body>
      <created-at type="datetime">2007-04-01T04:01:56-04:00</created-at>
      <id type="integer">2</id>
      <user-id type="integer">2</user-id>
    </post>
  </posts>
</user>

To see some real live examples, the Beast forum is currently implenting some of ActiveResource. Here’s technoweenie’s User account, in XML, and an XML list of selected Users. Pretty much any URL in Beast can have “.xml” appended to it.

ActiveResource Reference

Taking ARes Out for a Test Drive—Great introduction to ActiveResource, by one of its authors. ActiveResource and Testing—A post I made here discussing how I tested ActiveResource models. ActiveResource’s Subversion Repository—Current ActiveResource trunk, at svn.rubyonrails.org.

Thanks

Thanks go to Chad for the original idea, and Jared for writing Jester’s tests.

Jester is new, so we’d love to hear feedback on its strengths and weaknesses. We’re using it ourselves, so it’s under active development and getting plenty of love and attention. Please tell us what you think!