Add a threshold option

[tobie]

Johnn-Five implements a treshold attribute which determines the amount of change necessary of the value of the sensor to trigger a change event. Given we want to support sensors with multiple values, we'd at least need to add an attribute for each value. It might be simpler to add a method that would compare the current values with the last emitted ones and return a boolean (which would be used internally to decide whether or nor to trigger the change event). So for example setting up a geoloc sensor to only trigger when changing hemisphere:

new Sensor({
    change: function(prev, curr) {
        return Math.sign(prev.latitude) !== Math.sign(curr.latitude);
    }
});

[domenic]

Idle idea, not sure if it's a good one: add the following to your proposal.

new Sensor({
  change: Sensor.threshold(5, "latitude")
});

new Sensor({
  change: Sensor.threshold(5) // defaults to "value"
});

[tobie]

Has been tentatively included in the spec, though not properly spec'ed out yet.