hal

Hypertext Application Language

npm install hal
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HAL is a hypermedia-aware serialization format, which can be represented using JSON and XML format.

It's obviously particularly useful for RESTful API delivering real Hypermedia contents (cf HATEOAS).

Usage

In your browser

<script src="/path/to/hal.js"></script>
<script>
var resource = new hal.Resource({name: "Harry"}, '/harry');
resource.link('hello', '/harry/hello');
console.log(resource.toJSON());
</script>

Compatibility

Don't know, didn't test. It may not even work on the browser, who knows ?

OK, more seriously you'll require:

  • JSON.stringify
  • Array.prototype.forEach
  • Array.prototype.reduce
  • Object.prototype.hasOwnProperty

In Node.JS

npm install hal
var hal = require('hal');

var resource = new hal.Resource({name: "Harry"}, '/harry');
resource.link('hello', '/harry/hello');
console.log(resource.toJSON());

API

Resource (object, uri)

This class designs a HAL resource:

  • object are the base fields of this resource
    • Note that you can define _links and _embedded properties, this is at your own risks
    • If you set href property and uri is undefined, it will be used instead of uri and deleted
  • uri is the link to this property (as <link rel="self">)

This class designs a HAL link:

  • rel is mandatory
  • href or attributes.href is mandatory

Adds a new link to resource.

Resource#embed (rel, resource[s] [, pluralize])

Embeds other resource(s) to current resource.

Resource#toXML ()

Returns XML representation.

Note: embedded resources rel will be naively singularized by removing last 's'. See Resource#toJSON for more information.

Resource#toJSON ()

Returns JSON representation.

Note: rel will be naively pluralized by appending a 's' if there is not. This is due to differences between JSON and XML representation on embedded relationship and rel attribute.

Why this crappy singular/plural management ?

I base myself on the examples provided here. The two representations are equivalent, and you can see how plural and singular is used:

{
  "_links": {
   "self": { "href": "/orders" }
  },
  "_embedded": {
   "orders": [{
       "_links": {
         "self": { "href": "/orders/1" }
       }
     },{
       "_links": {
         "self": { "href": "/orders/2" }
       }
    }]
  }
}
<resource href="/orders">
  <resource rel="order" href="/orders/1">
  </resource>
  <resource rel="order" href="/orders/2">
  </resource>
</resource>

If this ugly action is the result of a misunderstanding, please let me know as I'd be glad to remove it!

Example

// A resource
var ordersCollection = new hal.Resource({
  currentlyProcessing: 14,
  shippedToday: 20
}, "/orders");

// Links
ordersCollection.link("next", "/orders?page=2");
ordersCollection.link("find", {href: "/orders{?id}", templated: true});

// Another resource
var order123 = new hal.Resource({
  total: 30.00,
  currency: "USD",
  status: "shipped"
}, "/orders/123");
// Alternative ways to link
order123.link(new hal.Link("basket", "/baskets/98712"));
order123.link(new hal.Link("customer", {href: "/customers/7809"}));

// Yet another resource
var order124 = new hal.Resource({
  total: 20.00,
  currency: "USD",
  status: "processing"
}, "/orders/124");
order124.link("basket", "/baskets/97213");
order124.link("customer", "/customers/12369");

// Embed the resources
ordersCollection.embed("orders", [order123, order124]);

Calling ordersCollection.toJSON(' '):

{
  "currentlyProcessing": 14,
  "shippedToday": 20,
  "_links": {
    "self": {
      "href": "/orders"
    },
    "next": {
      "href": "/orders?page=2"
    },
    "find": {
      "href": "/orders{?id}",
      "templated": "true"
    }
  },
  "_embedded": {
    "orders": [
      {
        "total": 30,
        "currency": "USD",
        "status": "shipped",
        "_links": {
          "self": {
            "href": "/orders/123"
          },
          "basket": {
            "href": "/baskets/98712"
          },
          "customer": {
            "href": "/customers/7809"
          }
        }
      },
      {
        "total": 20,
        "currency": "USD",
        "status": "processing",
        "_links": {
          "self": {
            "href": "/orders/124"
          },
          "basket": {
            "href": "/baskets/97213"
          },
          "customer": {
            "href": "/customers/12369"
          }
        }
      }
    ]
  }
}

Calling ordersCollection.toXML(' '):

<resource href="/orders">
  <link rel="next" href="/orders?page=2" />
  <link rel="find" href="/orders{?id}" templated="true" />
  <currentlyProcessing>14</currentlyProcessing>
  <shippedToday>20</shippedToday>
  <resource rel="order" href="/orders/123">
      <link rel="basket" href="/baskets/98712" />
      <link rel="customer" href="/customers/7809" />
      <total>30</total>
      <currency>USD</currency>
      <status>shipped</status>
  </resource>
  <resource rel="order" href="/orders/124">
      <link rel="basket" href="/baskets/97213" />
      <link rel="customer" href="/customers/12369" />
      <total>20</total>
      <currency>USD</currency>
      <status>processing</status>
  </resource>
</resource>

Yes, JSON seems a lot more verbose, but it's because of the spaces. In production you won't add indentation and then JSON is 517 bytes long, versus 625 bytes of XML.

Not yet, XML, not yet.

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