javascript setMonth() - setting a month to date2 from date1. Why also date1 change?

Question

I know, title isn't probably clear, but I have this code:

 var date1=new Date(); alert(date1); var date2=date1; alert(date2); date2.setMonth(date1.getMonth() + 6); alert(date1+" - "+date2); 

Why date1 change? I think date1 should remain the current date and date2 six months later ...

Thanks

Answer 1

Dates are objects in JavaScript. When you set date2=date1 , both date1 and date2 will reference the same object. Since they are both references to the same date object, the object may be updated or inspected using either.

Answer 2

Both the variables are pointing to same date object. You can do this instead

var date1=new Date();
alert(date1);
var date2=new Date(date1.valueOf());
alert(date2);
date2.setMonth(date1.getMonth() + 6);
alert(date1+" - "+date2);

In this approach, I am creating new object using values of existing one. Now there are two objects being point by different variables.

While you had assigned same object to both variables.

Answer 3

因为date2获取对date1的引用，而不是值。