Is there native support for implementing object arithmetic in Javascript?

Question

Think of the Date() object:

thisDate = new Date()
thatDate = new Date()
thisDate - thatDate //returns some date object

Would it be possible for me to make some object, say Clovers() such that:

theseClovers = new Clovers();
theseClovers.count = 10;
thoseClovers = new Clovers();
thoseClovers.count = 4;

theseClovers - thoseClovers; //returns b = new Clovers(); b.count = 6

This is the way I envisage it (but is entirely hypothetical):

function Clovers(){
    onSubtract(b){
        if(b instanceOf someClass){
            return this.count - b.count
        }
    }
}

You can add a .valueOf() function to your objects (or a prototype); it's like .toString() except for numbers. — Pointy
– Pointy, Commented Feb 5, 2017 at 15:32
Possible duplicate of Overloading Arithmetic Operators in JavaScript? — Karl-Johan Sjögren
– Karl-Johan Sjögren, Commented Feb 5, 2017 at 15:42

Jonas Wilms · Accepted Answer · 2017-02-05 15:48:00Z

2

function Clovers(val){
   this.count=val || 0;
}
Clovers.prototype.valueOf=function(){
 return this.count;
};

So it would work quite similar:

alert(new Clovers(new Clovers(10)-new Clovers(5)).count);
//or long written:
var a=new Clovers(10);
var b=new Clovers(4);
var c=new Clovers(a-b);
alert(c.count);

However, it might be better to have a custom addition function for that, similar to Array.prototype.concat:

 Clovers.prototype.concat=function(clover){
   return new Clovers(this.count-clover.count);
 };

Use like this:

var a=new Clovers(10);
var b=new Clovers(5);
var c=a.concat(b);
alert(c.count);

Thanks to Pointy and Karl-Johan Sjögren for the ideas...

edited Feb 5, 2017 at 15:48

answered Feb 5, 2017 at 15:42

Jonas Wilms

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2 Comments

Sancarn Over a year ago

I actually prefer the first technique of overloading valueOf(). This is exactly how Date appears to work since Date()-Date() actually returns a value. So this is perfect! Thanks for the fish!

Jonas Wilms Over a year ago

@Sancarn youre welcome ;) . please mark it as answer... and by the way, its not really overloading, its overriding

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