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);
3 Answers
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
2 Comments
Ionuț G. Stan
Nitpicking, but you could have used an object literal. Or, to stick to the original question, create a constructor and define
valueOf on the prototype. +1 otherwise.
Augustus Kling
@Ionuț G. Stan: You could use any construct that results in an object with a defined
valueOf method. Actually, my example uses a constructor (without a name) to create a valueOf method per object. You could have created the method within the prototype to share it across instances but I wanted to keep it as simple as possible and use a constructor.Create a function, which changes the this property. After defining the function using function(){}, add methods to it using prototype.
Normally, an instance of a function created using the new keyword will return an Object, which reprsents the this inside the defined function. When you define a toString method, the function will show a custom string when called from within a string context (default [object Object].
Example:
function MyClass(value){
this.value = value
this.init_var = 1;
}
MyClass.prototype.getInitVar = function(){
return this.init_var;
}
MyClass.prototype.setInitVar = function(arg_var){
this.init_var = arg_var;
}
MyClass.prototype.toString = function(){
return "This class has the following property: " + this.init_var;
}
var class_instance = new MyClass();
class_instance.setInitVar(3.1415);
alert(class_instance)
6 Comments
Rob W
toString is called when valueOf doesn't exist. Augustus's solution isn't portable, as it does not make use of prototypes.Augustus Kling
@Rob W: I think it was important to have an object returning a number (see the plus within the alert in the question). You need
valueOf for this purpose. Regarding portability it should not matter if you define the method on an object directly or on its prototype. I would be interested to learn which portability issues can arise because I can't think of any.Rob W
@AugustusKling You're defining the methods of the class from within the function, which you immediately initialise. It's not possible to create a new instance of the class. There's neither a way to extend the prototype of the class, because it has already been initialised at definition.
|
Here is the solution,
var MyObject = Date;
var b= new MyObject();
alert(+b) //It will display the current date in milliseconds;
Hope this helps you.
1 Comment
Felix Kling
I think the OP wants to the create his own object, which is converted to some numerical value. He does not want it to be
Date.