Encapsulating Complex Calculation in JavaScript

Question

This is code for performing a calculation that should be repeated with different levels and temperatures. I am concerned about the organization of this code as I feel it may contain too many helper functions and seems a little unnecessarily complicated. Only the getCharge() method needs to be exposed to the browser.

There is sample usage of this code after the initial definition.

var hprVessel = function (level, temp) {
/**
* @params {Number} level - Percentage load for HPR 
* @params {Number} temp - temperature of fluid
*/
    var liquidCoefficients = [
        83.4485407734612,
        -0.111449280945489,
        0.000100022560084721,
        -0.00000206240663899928
    ];

    var vaporCoefficients = [
        0.895329190066827, 
        0.016635773286873, 
        -0.0000894924196507015, 
        0.00000206296636296276
    ];

    var vessel = {
        // Vessel-specific Params
        diameter: 1.9583 * level,
        height: 0.2937 * level,
        length: 15.9583 * level,

        // Calculations
        getLiquidVol: function () {     
            var r = this.diameter/2;
            var sectionArea = Math.pow(r, 2) * Math.acos((r - this.height) / r);
            var triangleArea = Math.sqrt(Math.pow(r, 2) - Math.pow((r-this.height), 2))*(r-this.height);

            return (this.length * sectionArea * triangleArea);
        },
        getVesselVol: function () {
            return (Math.PI * Math.pow(this.diameter, 2) * this.length);
        },
        getVaporVol: function () {
            return (vessel.getVesselVol() - vessel.getLiquidVol());
        },
        getLiquidCharge: function (temp) {
            return (vessel.getLiquidVol() * vessel.calcDensity(liquidCoefficients, temp));
        },
        getVaporCharge: function (temp) {
            return (vessel.getVaporVol() * vessel.calcDensity(vaporCoefficients, temp));
        },
        chargeHPR: function (temp) {
            return (1000 + vessel.getLiquidCharge(temp) + vessel.getVaporCharge(temp));
        },

        // Helper functions
        calcDensity: function (regressionCoefs, temp) {
            var liqDensityArray = regressionCoefs.map(function (coef) {
                return coef * Math.pow(temp, regressionCoefs.indexOf(coef));
            });

            return vessel.sum(liqDensityArray);
        },
        sum: function (arr) {
            return arr.reduce( function (prev, current) {
                return (prev + current);
            }
        }
    };

    return {
        getCharge: function() {
            return vessel.chargeHPR(temp);
        }
    };
}

var vessel = hprVessel(1, -30);
var result = vessel.getCharge();

Answer 1

diameter: 1.9583 * level,
height: 0.2937 * level,
length: 15.9583 * level,

It might be wise to actually put these numbers in a constant and naming them appropriately. That way, in the long run, you won't forget what these values are.

return (/* stuff */);

I notice you also use parens in your returns. Unless they're a personal preference, they're actually optional (What do you think this is? PHP? :P)

Now this code appears to benefit more using prototypal inheritance rather than a factory pattern. That's because every time you call hprVessel, it builds an object of functions. With prototypal inheritance, your instance will only hold instance properties, aka "vessel-specific data". The functions will be shared across your vessel instances via the prototype.

Here's a short example:

function HPRVessel(level, temp){

  // Instance data, aka vessel-specific data
  this.temp = temp;
  this.level = level;
  this.diameter = HPRVessel.SOME_CONSTANT * level,
  this.height = HPRVessel.ANOTHER_COSNTANT * level,
  this.length = HPRVessel.YET_ANOTHER_CONSTANT * level,

}

// pseudo-static properties
// Here we append general HPRVessel constants
HPRVessel.liquidCoefficients = [
  83.4485407734612,
  -0.111449280945489,
  0.000100022560084721,
  -0.00000206240663899928
];

HPRVessel.SOME_CONSTANT = 1.9583
HPRVessel.ANOTHER_COSNTANT = 0.2937
HPRVessel.YET_ANOTHER_CONSTANT = 15.9583

// Here, we define shared stuff. Best practice is to just put methods on it.
HPRVessel.prototype.getCharge = function(){
  // Anything on the instance is accessible via `this`
  return this._chargeHPR(this.temp);
};

// Since there's no "private", we use the convention of prefixing `_` to tell
// curious people not to call these methods directly
HPRVessel.prototype._chargeHPR= function(){
  return (1000 + this._getLiquidCharge(this.temp) + this._getVaporCharge(this.temp));
};

// Usage:
var vessel = new HPRVessel(1, -30);
var result = vessel.getCharge();