Module development - using example of Temperature Nodes with 1-Wire PT100 / DS18B20 Sensor at multiple Locations

As mentioned in the previous post, the string containing a complete module can be pretty big and could lead to run out of memory. Therefore the question:

How can a module be broken up into small(er) pieces and composed at runtime from such pieces.

In order to have the a piece of code working as a module, it is good enough to have a 'hock object' as the first or core component in the Modules cache to which more components can 'be attached' to. To attache components to a module core component, the module has to be required from the cache and then the components can 'be attached' to it. After all, the module - in this case the 'class'/prototype definition - is just a function object - one and the same whether in the cache or in the application code.

Since the constructor function is such a first and core component, let's try to attache a the .getTemp() as a component.

Intentionally, the module was retrieved into a temporary variable tempTemp - line 37 - to prove that the module is the very same object that is later retrieved into the original variable Temperature - line 57 - and includes now the complete Temperature 'class'/prototype definition.

The split up module code into core component - lines 4..34 - and other component(s) - lines 49/41..48 - and attaching the other component(s), such as a method method - line 40 - represents composing a complete module from components component by component. The code for it looks like this:

// TemperatureDevTest2.js

require("DS18B20"); // used by the dynamically loaded module
Modules.addCached("Temperature",`
// Temperature.js
// 'class' (Prototype definition)
var Temperature = function // module (class), for multiple instances
  ( name      // name hinting room / location of sensor\
  , oneWire   // one-wire; for example: new OneWire(B8);
  , addr      // address on the one-wire (required for multiples)
  , interval  // interval in milliseconds of measurements
  , preferred // optional, unit - "C" or "F" (default and not F is C)
  ) {
  // set givens
  this.name       = name;
  this.oneWire    = oneWire;
  this.addr       = addr;
  this.interval   = interval;
  this.preferred  = (preferred==="F") ? "F" : "C";
  this.enabled    = (typeof enabled === "undefined") || enabled;
  this.t = (this.preferred==="C") ? 0 : 32; // set current to 'frozen'
  this.intervalId = null; // later also used as indicator for enabled
  this.sensor     = null; // laster also used as indicatore for connected
  // get going
  this.sensor = require("DS18B20").connect(this.oneWire)­;
  this.intervalId = setInterval(function(_this) {
      _this.sensor.getTemp(function(t) {
      _this.t = t;
    });
  }, this.interval, this);
};

exports = Temperature;
`);

// require the Temperature module into a temporary tempTemp var:
var tempTemp = require("Temperature");

// attach the .getTemp() method
tempTemp.prototype.getTemp = function
( unit // optional, unit "F" or "C", default "C"
) {
  var u = ((typeof unit !== "undefined") && (unit === "F")) ? "F" : "C";
  var d = (u === "F")
    ? (this.t * 1.8) + " Fahrenheit"
    : this.t + " Celsius";
  return d;
};


// usage

// setup oneWire
var oneWire = new OneWire(B8);

// setup 1st temperature sensor ts1
var Temperature = require("Temperature");
var ts1 = new Temperature
  ( "office" // name / location of temperatre sensor 1
  , oneWire
  , null     // addr on one-wire currently not implemented / used
  , 5000     // every 5 secs make a read (to keep it not booring)
  , "F"      // preferred unit is Fahrenheit
  );


// for sample's sake, do everhthing deferred for more 
// than 5 seconds in order to have value(s) to display
setTimeout(function(){

// get temp in preferred unit 
console.log(ts1.getTemp());

},6000);

There is one comment to make: if the to-attach module component is retrieved over the network or read from a storage it is retrieved as a string and not as an object... but that is no issue what so ever... we just 'ab-use' the Modules.addCached(...) and require(...) infrastructure as a stepping stone:

• add the to-attach component to the Modules cache as a module with Modules.addCached(...) - lines 36..49.
  
• retrieve the to-attach component as module from the Modules cache with require() - line 55.
  
• attach it to the core module retrieved from the Modules cache as done before - line 55.
  
  

The code with all module components as strings looks then like:

// TemperatureDevTest2.js

require("DS18B20"); // used by the dynamically loaded module
Modules.addCached("Temperature",`
// Temperature.js
// 'class' (Prototype definition)
var Temperature = function // module (class), for multiple instances
  ( name      // name hinting room / location of sensor\
  , oneWire   // one-wire; for example: new OneWire(B8);
  , addr      // address on the one-wire (required for multiples)
  , interval  // interval in milliseconds of measurements
  , preferred // optional, unit - "C" or "F" (default and not F is C)
  ) {
  // set givens
  this.name       = name;
  this.oneWire    = oneWire;
  this.addr       = addr;
  this.interval   = interval;
  this.preferred  = (preferred==="F") ? "F" : "C";
  this.enabled    = (typeof enabled === "undefined") || enabled;
  this.t = (this.preferred==="C") ? 0 : 32; // set current to 'frozen'
  this.intervalId = null; // later also used as indicator for enabled
  this.sensor     = null; // laster also used as indicatore for connected
  // get going
  this.sensor = require("DS18B20").connect(this.oneWire)­;
  this.intervalId = setInterval(function(_this) {
      _this.sensor.getTemp(function(t) {
      _this.t = t;
    });
  }, this.interval, this);
};

exports = Temperature;
`);

// add .getTemp() method as moduleComponent to the Modules cache
Modules.addCached("moduleComponent",`
var moduleComponent = function
( unit // optional, unit "F" or "C", default "C"
) {
  var u = ((typeof unit !== "undefined") && (unit === "F")) ? "F" : "C";
  var d = (u === "F")
    ? (this.t * 1.8) + " Fahrenheit"
    : this.t + " Celsius";
  return d;
};

exports = moduleComponent;
`);

// require the Temperature module into a temporary tempTemp var:
var tempTemp = require("Temperature");

// require and attach the .getTemp() method as module component
tempTemp.prototype.getTemp = require("moduleComponent");

// usage

// setup oneWire
var oneWire = new OneWire(B8);

// setup 1st temperature sensor ts1
var Temperature = require("Temperature");
var ts1 = new Temperature
  ( "office" // name / location of temperatre sensor 1
  , oneWire
  , null     // addr on one-wire currently not implemented / used
  , 5000     // every 5 secs make a read (to keep it not booring)
  , "F"      // preferred unit is Fahrenheit
  );


// for sample's sake, do everhthing deferred for more 
// than 5 seconds in order to have value(s) to display
setTimeout(function(){

// get temp in preferred unit 
console.log(ts1.getTemp());

},6000);

...and works - and we get two (2) warnings about module not found on upload as expected... of course it runs... no magic... just JavaScript brilliantly and to it's true nature implemented by @Gordon.