EventSource Realtime data feed

Javascript has a widely available but not well known feature called EventSource() or 'Server Sent Events' (SSE). You can read more about these here. The file WebUi.js opens an event source connection and uses these updates to generate the onMessage events that are sent to your javascript.

If you are not using WebUi.js and are directly interfacing then you probably want to create an EventSource() to receive updates. However there are maximum connection limitations around using eventsource, so you should open these sparingly. If you've never used EventSource before there are some samples at the end of this page using both EventSource() and fetch()

Requesting an Event Source

The following query arguments are available

Name	Purpose
format	Event Format. Requests event stream data to be delivered in an alternative format. The default format is JSON
want	A comma seperated list of event data you wish to receive. The default value is "sale" which indicates the event source is being used to runnnig or monitoring active sales
session	Required. Supplies the session identifier for where events are to be sourced from.

Contents of the Source

All event type names are in lowercase unless specifically documneted. There are some mixed case event types which are used for rare or more diagnostic type messages

sale

Sent whenever the POS engine determines the sale may have changed.

usermessage

Indicates a display message, simple yes/no style prompt or error message that should be displayed to the user. See Override UserMessage

userprompt

Indicates a request to ask the user for more information. See Override UserPrompt

barcode

Indicates a barcode has been scanned, giving you the option to process it (Note. Contact Fieldpine before using this event, it may be changing internally)

Field	Purpose
RawScan	The raw barcode scan data
Owner	Indicates the owning session for this scan. Scan advisories are sent to all subscribers and this field indicates if you should process this message or not 0 - You are receiving this message as an advisory and can ignore it 1 - This message is for you to display and process 2 - This message is being sent to multiple subscribers. It isn't clear to the Pos Engine which session should receive this advice
TypeCode	A numeric value indicating the type of barcode this appears to be
TypeStr	A string value equivalent of TypeCode

The Last-Event-Id is set to the RVE of the records change date/time in UTC. This means it will be a value in the format YYYYMMDD.HHmmSSCCC

Using EventSource from Javascript

EventSource themselves are incredibly easy to work with, simply open a URL and wait for events to be dispatched to you. The downside is that you cannot add extra HTTP headers or make other adjustments.

    // Create the event source
    var evtsrc = new EventSource("/eventsource?session=????");

    // Create a handler for sale
    // This is triggered whenever a sale update is sent from the server
    evtsrc.onsale = function (oo) {
        // oo is a MessageEvent
        if ((oo.data.length > 4) && (oo.data[0] === '{')) {
            try {
                // Your code here....
            } catch (_) {
                ;
            }
        }
    };

If you need to add HTTP headers, then you can use fetch streams instead