changed

 

Polls HTTP resources and fires events when they change.

Features

* Supports HTTP and HTTPS
* Transparently decodes gzipped resources

Installation

``
npm install robinjmurphy/changed
`

Usage

`javascript
var changed = require('changed-http');

var resource = new changed.Resource('http://www.example.com');

resource.on('changed', function (current, previous) {
console.log('Resource changed. Response body was ' + previous + ' , is now ' + current + '.');
});

resource.startPolling(5000);
`

API

#### new changed.Resource(url, options)

##### Parameters

* url - _string_
* options - _object_ - configuration options

##### Options

The options object supports all of the standard options from http.request and https.request. In addition, it supports the following properties:

* compare - _function_ - overrides the default response body comparison. Receives the current response body as its first argument and the previous response body as its second argument. Should return true if the responses differ.

---

#### .startPolling(interval)

Start polling the resource for changes.

##### Parameters

* interval - _number_ - the interval time in milliseconds (default 10000)

---

#### .stopPolling()

Stop polling the resource.

---

$3

##### changed

Fired when the resource's body changes.

`javascript
resource.on('changed', function (current, previous) {
// current is a string containing the curent response body
// previous is a string containing previous response body
});
`

##### error

Fired when an error occurs.

`javascript
resource.on('error', function (error) {
// error is an Error object
});
`

##### response

Fired each time a response is received whilst polling.

`javascript
resource.on('response', function (body, res) {
// body is a string containig the response body
// res is the http/https response object
});
`

Logging

All polling requests are logged using console.info by default. To use a custom logger, like Winston, just set the changed.logger property:

`javascript
var changed = require('changed-http');
var winston = require('winston');

changed.logger = winston;
`

Examples

$3

In the following example the changed event is only fired when the foo property in a JSON response changes.

`javascript
var changed = require('changed-http');

var resource = new changed.Resource('http://www.example.com/some/json/file.json', {
compare: function (current, previous) {
var currentJson = JSON.parse(current);
var previousJson = JSON.parse(previous);

return (currentJson.foo !== previousJson.foo);
}
});

resource.startPolling(5000);
``