Question

I wonder how is it possible to create an object for example MyObject() which it can act like javascript Date object when we +(new MyObject()) like:

var a = new Date();
alert(+a);

Answer 1

Your object needs to have a valueOf method like so:

var f=new function(){
    this.valueOf=function(){
        return 5;
    }
};
alert(+f); // Displays 5

If you don’t want to define the method on the object but on its prototype as the comments suggested, use the following:

function MyObject(value){
    this.value = value;
}
MyObject.prototype.valueOf = function(){
    return this.value
}

var o = new MyObject(17);
alert(+o); // Displays 17