constructor within a constructor in javascript?

Question

I want a constructor within a constructor- I've searched stackoverflow and googled extensively......

I have a constructor RentalProperty:

function RentalProperty(numberOfUnits, address, dateAcquired, acCost, isFinanced,                
loanAmount){
this.numberOfUnits = numberOfUnits;
this.address = address;
this.dateAcquired = new Date(dateAcquired);
this.acCost = acCost;
this.isFinanced = isFinanced; 
this.loanAmount = 0;   
this.newValue = 0;
this.equity = function(){
    if (this.newValue === 0){
        return (this.acCost - this.loanAmount);
    } else {
        return (this.newValue - this.loanAmount);
    }
 };
}

Each instance of RentalProperty will have a series of unit objects that I would like to be unit1, unit2, unit3, etc. However some instances of RentalProperty will have only one unit while others may have six, twelve, or more. The way I'm doing it here doesn't seem right as there is a lot of repetition of code and I will need to make a large number of unit objects that may not be used for a particular instance of RentalProperty:

RentalProperty.prototype.unit1 = {
unitNumber : "1",
monthlyRent: 0,
leaseStart: new Date(0),
leaseEnd: new Date(0),
numBeds: 0, 
isSec8: false,
tenantPortion: 0,
sec8Portion: 0
};

RentalProperty.prototype.unit2 = {
unitNumber : "2",
monthlyRent: 0,
leaseStart: new Date(0),
leaseEnd: new Date(0),
numBeds: 0,
isSec8: false,
tenantPortion: 0,
sec8Portion: 0
};

RentalProperty.prototype.unit3 = {
unitNumber : "3",
monthlyRent: 0,
leaseStart: new Date(0),
leaseEnd: new Date(0),
numBeds: 0,
isSec8: false,
tenantPortion: 0,
sec8Portion: 0
};

I tried various combinations of syntax (I've been pulling my hair out for hours) to put a unit constructor within the RentalProperty constructor with code such as:

....
this.unit["for(i=0, i < this.numberOfUnits, i++){return i;}"] = {
    unitNumber : "i",
    monthlyRent: 0,
    leaseStart: new Date(0),
    leaseEnd: new Date(0),
    numBeds: 0, 
    isSec8: false,
    tenantPortion: 0,
    sec8Portion: 0
    };

....hoping that this would create the correct number of units using the value of the this.numOfUnits property of RentalProperty but it gives me "missing operand".

I have also tried:

....//'new Object' added
this.unit[for(i=0, i < this.numberOfUnits, i++){return i;}] = new Object{
    unitNumber : "i",
    monthlyRent: 0,
    leaseStart: new Date(0),
    leaseEnd: new Date(0),
    numBeds: 0, 
    isSec8: false,
    tenantPortion: 0,
    sec8Portion: 0
    };
....

....//trying to make another constructor
function Units(){
unitNumber = "1";
monthlyRent = 0;
leaseStart = new Date(0);
leaseEnd = new Date(0);
numBeds = 0;
isSec8 = false;
tenantPortion = 0;
sec8Portion = 0;
}

var yale = new RentalProperty()

var yale.unit33 = new Units();

....but when I try to make an instance of the new Units class with the RentalProperty instance before it in dot notation it says 'Unexpected Token'.

I have only been learning to code for 2 months (approx one month each of html and javascript) so I'm pretty sure this is a noob question. Any help would be much appreciated..... This is also my first stackoverflow question so please accept my apologies if my formatting is off.

Bergi- it says "unexpected token" in my IDE results pane (lol- I'm such a noob I don't know if that's the right terminology!) — CoolestUsername, Aug 27 '13 at 20:19
I meant "*What line, what code?*" not "*On which screen*" :-) — Bergi, Aug 27 '13 at 20:21
Strange that you put instance specific members on the prototype but non instance specific memmbers (equity method) in the constructor body. It should be the other way around. As other people have answered the unit member should be an array of units (this.units) and you can define `Rentalproperty.prototype.addUnit, removeUnit, findUnit ...` functions to manipulate them. More on prototype here: http://stackoverflow.com/questions/16063394/prototypical-inheritance-writing-up/16063711#16063711 — HMR, Aug 28 '13 at 00:34

Bergi · Accepted Answer · 2013-08-27T19:30:49.273

It seems like you want

this.units = []; // an array which
for (var i=0; i < this.numberOfUnits; i++) { // in a loop
    this.units[i] = { // is filled with objects
        unitNumber : i,
        monthlyRent: 0,
        leaseStart: new Date(0),
        leaseEnd: new Date(0),
        numBeds: 0, 
        isSec8: false,
        tenantPortion: 0,
        sec8Portion: 0
    };
}

Of course instead of the object literal you also can use new Units(i) or something to create the unit objects.

If you don't want an array, but make numbered properties on your object (I'd discourage from that) it would be

this["unit"+i] = …

Paul S. · Answer 2 · 2013-08-27T19:32:08.833

Just consider a completely independent constructor for Unit

RentalProperty.Unit = function Unit(i) {
    if (undefined === i) i = 1;
    this.unitNumber = '' + i;
    this.monthlyRent = 0;
    this.leaseStart = new Date(0);
    this.leaseEnd = new Date(0);
    this.numBeds = 0;
    this.isSec8 = false;
    this.tenantPortion = 0;
    this.sec8Portion = 0;
};

I put it as a property of RentalProperty to keep everything neat.
Next generate all your units in your RentalProperty constructor, or however..

this.units = [];
var i;
for (i = 0; i < this.numberOfUnits; ++i) {
    this.units.push(new RentalProperty.Unit(i));
}

Doing it this way also means you can set up a prototype chain for Unit, should you desire to, and you can confirm that a unit u is indeed a Unit using u instanceof RentalProperty.Unit.

score 1 · Answer 3 · answered Aug 27 '13 at 19:25

You are overcomplicating things. As long as there is a Unit constructor already defined you can just do:

function RentalProperty(numberOfUnits){
    this.numberOfUnits = numberOfUnits;
    this.units = [];
    for (var i = 0; i < numberOfUnits; ++i) {
       this.units.push(new Unit(i));
    }
}

This constructor can be globally scoped, as in

function Unit(unitNumber) {
    this.unitNumber = unitNumber;
}

or you can also make it a property of RentalProperty:

RentalProperty.Unit = function(unitNumber) {
    this.unitNumber = unitNumber;
}

in which case you would create units with new RentalProperty.Unit(i).

score 0 · Answer 4 · answered Aug 28 '13 at 00:51

The question has been answered several times but here is the full code.

function Unit(rentProp){
  this.unitNumber = ""+(rentProp.units.length+1);
  this.rentalProperty=rentProp
  //all of the foolowing props could go on prototype
  //because the constructor fills them only with default values
  //later you'll assign new values to them with
  //someUnitInstance.monthlyRent=... 
  this.monthlyRent = 0;
  this.leaseStart = null;
  this.leaseEnd = null;
  this.numBeds = 0;
  this.isSec8 = false;
  this.tenantPortion = 0;
  this.sec8Portion = 0;
}

function RentalProperty(numberOfUnits, address
 , dateAcquired, acCost, isFinanced
 ,loanAmount){
  this.numberOfUnits = numberOfUnits;
  this.address = address;
  this.dateAcquired = new Date(dateAcquired);
  this.acCost = acCost;
  this.isFinanced = isFinanced;
  this.units=[];
};
//default values on prototype, assuming you're not using
//hasOwnProperty later to iterate through properties because
//defaults (on prototype) won't show up
RentalProperty.prototype.loanAmount = 0;   
RentalProperty.prototype.newValue = 0;
RentalProperty.prototype.equity = function(){
  if (this.newValue === 0){
    return (this.acCost - this.loanAmount);
  } else {
    return (this.newValue - this.loanAmount);
  }
};
RentalProperty.prototype.addUnit = function(){
  this.units.push(new Unit(this));
}

var r=new RentalProperty();
r.addUnit();
r.addUnit();
console.log(r.units);

constructor within a constructor in javascript?

4 Answers4