如何创建像Date（）这样的JavaScript对象？

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

Answer 2

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)

Answer 3

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.