prototype.Function is not being exported in node.js

Question

I found this javascript Kalman filter library online and I wanted to use it with my node.js application. As I wanted to include this js file into my node.js application, I tried to export the required functions ( added module.exports as shown below) .

module.exports = {

  KalmanModel : function(){

    function KalmanModel(x_0,P_0,F_k,Q_k){
      this.x_k  = x_0;
      this.P_k  = P_0;
      this.F_k  = F_k;
      this.Q_k  = Q_k;
    }

    KalmanModel.prototype.update =  function(o){
      // code 
    }

    return KalmanModel;
  },

  KalmanObservation : function(){

    function KalmanObservation(z_k,H_k,Q_k){
      this.z_k = z_k;//observation
      this.H_k = H_k;//observation model
      this.R_k = R_k;//observation noise covariance
    }

    return KalmanObservation;
  }
};

But when I try to run the following piece of code

Code:

var kal =require('./kalman');
var observationVal = observationValues;
var x_0 = $V([observationVal[0]]);
var P_0 = $M([[2]]);
var F_k=$M([[1]]);
//process noise
var Q_k=$M([[0]]);
var KM = kal.KalmanModel(x_0,P_0,F_k,Q_k);
//value we measure
var z_k = $V([observationVal[0]]);
var H_k = $M([[1]]);
var R_k = $M([[4.482]]);
var KO = kal.KalmanObservation(z_k,H_k,R_k);

for (var i=1;i<10;i++){
z_k = $V([observationVal[i]]);
KO.z_k=z_k;
KM.update(KO);

I get an error

TypeError: object is not a function.

It looks like method defined with prototype is not getting exported. What am I doing wrong here?

Answer 1

I'm really struggling to understand why the top piece of code is written as it is (with named properties matching the same names as the function within)

My suggestions would be log out some variables to see what their value is.

Namely: kal , typeof kal , typeof kal.KalmanModel . Also, i think you need to create an instance of KalmanModel to use the prototype functions, so try:

var KM = new kal.KalmanModel(x_0,P_0,F_k,Q_k);

Answer 2

Well if you don't wanna change much in the existing source code you can do this. Don't remove the implicit function call ie : (function(){//code})(); and i think you should be set.

module.exports = {

    KalmanModel : (function(){

        function KalmanModel(x_0,P_0,F_k,Q_k){
          this.x_k  = x_0;
          this.P_k  = P_0;
          this.F_k  = F_k;
          this.Q_k  = Q_k;
        }

        KalmanModel.prototype.update =  function(o){
          // code 
        }

        return KalmanModel;
    })(),

    KalmanObservation : (function(){

        function KalmanObservation(z_k,H_k,Q_k){
          this.z_k = z_k;//observation
          this.H_k = H_k;//observation model
          this.R_k = R_k;//observation noise covariance
        }

        return KalmanObservation;
    })()
};

Or simply append the following in the library kalman.js

module.exports = {
    myKalmanModel : KalmanModel,
    myKalmanObservation : KalmanObservation
}

and access as

var KM = kal.myKalmanModel(x_0,P_0,F_k,Q_k);