Using ADBkit to return a prop value

I really do not understand these functions well (still learning) and all i am attempting to do is read ro.product.model from a device, and print the return to a variable fireOs;

Here is the syntax: client.getProperties(serial[, callback])

Retrieves the properties of the device identified by the given serial number. This is analogous to adb shell getprop.

serial The serial number of the device. Corresponds to the device ID in client.listDevices(). callback(err, properties) Optional. Use this or the returned Promise. err null when successful, Error otherwise. properties An object of device properties. Each key corresponds to a device property. Convenient for accessing things like 'ro.product.model'. Returns: Promise Resolves with: properties (see callback)

function getProp(prop){
client.listDevices()
.then(function(devices) {
return Promise.map(devices, function(device) {
  return client.getProperties(device.id, prop)
})
})
.then(function() {
fireOs = prop;
})
.catch(function(err) {
$('.fireos').text('Error: ', err)
})};

all im getting returned to fireOs however is prop ' r.product.model' instead of the actual return of that

Can someone see what im missing?