I was looking into how paper.js did their operator overloading and what I found was pretty clever:

var operators = {
'+': 'add',
'-': 'subtract',
'*': 'multiply',
'/': 'divide',
'%': 'modulo',
'==': 'equals',
'!=': 'equals'
};
function $eval(left, operator, right) {
var handler = operators[operator];
if (left && left[handler]) {
var res = left[handler](right);
return operator == '!=' ? !res : res;
}
switch (operator) {
case '+': return left + right;
case '-': return left - right;
case '*': return left * right;
case '/': return left / right;
case '%': return left % right;
case '==': return left == right;
case '!=': return left != right;
default:
throw new Error('Implement Operator: ' + operator);
}
}; |

var operators = {
'+': 'add',
'-': 'subtract',
'*': 'multiply',
'/': 'divide',
'%': 'modulo',
'==': 'equals',
'!=': 'equals'
};
function $eval(left, operator, right) {
var handler = operators[operator];
if (left && left[handler]) {
var res = left[handler](right);
return operator == '!=' ? !res : res;
}
switch (operator) {
case '+': return left + right;
case '-': return left - right;
case '*': return left * right;
case '/': return left / right;
case '%': return left % right;
case '==': return left == right;
case '!=': return left != right;
default:
throw new Error('Implement Operator: ' + operator);
}
};

Though technically this is PaperScript and not JavaScript, so they can get around the lack of native JS operator overloading. The PaperScript code is given a minimal compile pass which replaces calls to arithmetic operators with calls to `$eval()`

.

// PaperScript
var p = new Point(10, 20);
var r = p * 5;
// JavaScript
var p = new Point(10, 20);
var r = $eval(p, "*", 5); |

// PaperScript
var p = new Point(10, 20);
var r = p * 5;
// JavaScript
var p = new Point(10, 20);
var r = $eval(p, "*", 5);

Related PaperScript source

So as long as Point#multiply is defined then the operator is effectively overloaded.

I’m very interested in the implications for PixieEngine and CoffeeScript.