polling-to-event

node-polling-to-event

Receive events with EventEmitter from a polling function ran on an interval

Technically speaking polling is defined as status check from an external device, but with node-polling-to-event you can expect events from your own function that polls whatever resource you want that implies either a synchronous or an asynchronous operation.

Installation

$ npm install polling-to-event

Usage

var pollingtoevent = require("polling-to-event");

var emitter = pollingtoevent(function(done) {
  // your async stuff
  // ....
  done(null, arg1, arg2, ..., argN);
});

emitter.on("interval", function(data) {
  console.log(data);
});

emitter.on("err", function(err) {
  console.log(err);
});    

Example

var pollingtoevent = require("polling-to-event"),
  request = require("request");

var url = "https://raw.githubusercontent.com/mozilla/contribute.json/master/schema.json";

emitter = pollingtoevent(function(done) {
  request.get(url, function(err, req, data) {
    done(err, data);
  });
});

emitter.on("interval", function(data) {
  console.log("Event emitted at %s, with data %j", Date.now(), data);
});

emitter.on("error", function(err, data) {
  console.log("Emitter errored: %s. with data %j", err, data);
});

Long polling

If you set the option longpolling:true the emitter will emit an update event when the polled data differs.

emitter = pollingtoevent(function(done) {
  request.get(url, function(err, req, data) {
    done(err, data);
  });
}, {
  longpolling:true
});

emitter.on("update", function(data) {
  console.log("Update emitted at %s, with data %j", Date.now(), data);
});

API

pollingtoevent(pollingfunction, options)

It creates an event emitter that emits the polled data on an interval.

Your polling function will be called right away, and at the end of every interval.

Arguments

• pollingfunction(done) - Required. The function you want to be called at an interval. When called, this function will receive a done parameter as its last argument.
  • done(error, arg1, arg2, ... argN) - You must call done() inside your function when your function finish its work.
    • error - Required. Call done() with null as its first argument if there was no error. Call it with an error object instance as first argument if you wish the emitter to emit an error event..
    • arg1, arg2, ... argN - The data fetched by your polling function. Your pollingfunction passes this arguments to done() in order to be emitted by the emitter. Any number of arguments will do.
• options - Optional. An Object having any of the following keys:
  • interval - Interval in milliseconds. Default: 1000.
  • longpolling - Set to true if you want to be notified when data from the last poll differ from previous polled data. The data taken for comparison is every argument your pollingfunction passes to done(). The comparison is made with deep-equal. Default: false.
  • eventName - The event name to emit on each successful call to done(). Default: "interval".
  • eventUpdateName - The event name to emit when last polled data differs from previous polling data. Default: "update".

Returns

Returns an EventEmitter instance with some extra methods. See Methods.

Emitter events

• interval - Emitted when an interval has completed and the done() function was called with no errors. You can also customize this event's name using the option eventName. Parameters: Your listener gets the parameter passed to done() with exception of the error parameter which is the first parameter done() uses.
• error - Emitted when done() was called with an error object. It emits the data polled by your polling function. Parameters. An error object.
• update - Emitted when option longpolling is true and the last polled data differs from the previous polling data. Parameters: Your listener gets the parameter received by done() with exception of the error parameter which is the first parameter done() uses. You can also customize this event's name using the option updateEventName

Emitter methods

stop()

Stops the interval.

resume()

Resumes the interval if it has been stopped

TODO

• Add a default behaviour to poll URLs via a GET request if an URL string is passed as argument instead of a function.

License

The MIT License (MIT)

Copyright (c) 2015 osk <[e-mail]>

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.