Peter McG Peter McG - 2 months ago 8
Javascript Question

Overloading Arithmetic Operators in JavaScript?

This is the best way I can think of phrasing this question, given this JavaScript "class" definition:

var Quota = function(hours, minutes, seconds){
if (arguments.length === 3) {
this.hours = hours;
this.minutes = minutes;
this.seconds = seconds;

this.totalMilliseconds = Math.floor((hours * 3600000)) + Math.floor((minutes * 60000)) + Math.floor((seconds * 1000));
}
else if (arguments.length === 1) {
this.totalMilliseconds = hours;

this.hours = Math.floor(this.totalMilliseconds / 3600000);
this.minutes = Math.floor((this.totalMilliseconds % 3600000) / 60000);
this.seconds = Math.floor(((this.totalMilliseconds % 3600000) % 60000) / 1000);
}

this.padL = function(val){
return (val.toString().length === 1) ? "0" + val : val;
};

this.toString = function(){
return this.padL(this.hours) + ":" + this.padL(this.minutes) + ":" + this.padL(this.seconds);
};

this.valueOf = function(){
return this.totalMilliseconds;
};
};


and the following test setup code:

var q1 = new Quota(23, 58, 50);
var q2 = new Quota(0, 1, 0);
var q3 = new Quota(0, 0, 10);

console.log("Quota 01 is " + q1.toString()); // Prints "Quota 01 is 23:58:50"
console.log("Quota 02 is " + q2.toString()); // Prints "Quota 02 is 00:01:00"
console.log("Quota 03 is " + q3.toString()); // Prints "Quota 03 is 00:00:10"


Is there any way of implicitly creating
q4
as a
Quota
object using the addition operator as follows...

var q4 = q1 + q2 + q3;
console.log("Quota 04 is " + q4.toString()); // Prints "Quota 04 is 86400000"


rather than resorting to...

var q4 = new Quota(q1 + q2 + q3);
console.log("Quota 04 is " + q4.toString()); // Prints "Quota 04 is 24:00:00"


If not what are the best practice recommendations in this area for making custom numeric JavaScript objects composable via the arithmetic operators?

Dan Dan
Answer

As far as I'm aware, Javascript (at least as it exists now) doesn't support operator overloading.

The best I can suggest is a class method for making new quota objects from several others. Here's a quick example of what I mean:

// define an example "class"
var NumClass = function(value){
    this.value = value;
}
NumClass.prototype.toInteger = function(){
    return this.value;
}

// Add a static method that creates a new object from several others
NumClass.createFromObjects = function(){
    var newValue = 0;
    for (var i=0; i<arguments.length; i++){
        newValue += arguments[i].toInteger();
    }
    return new this(newValue)
}

and use it like:

var n1 = new NumClass(1);
var n2 = new NumClass(2);
var n3 = new NumClass(3);

var combined = NumClass.createFromObjects(n1, n2, n3);
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