date = new Date();d.valueOf() vs Date.now()

There are several ways to get the current time in JavaScript:

• new Date() creates a Date object representing current date/time
• new Date().valueOf() returns number of milliseconds since midnight 01 January, 1970 UTC
• new Date().getTime() Functionally equivalent to new Date().valueOf()
• Date.now() Functionally equivalent to the 2 methods above

As mentioned in the comments and MDN links, Date.now() is not supported in Internet Explorer 8. So if IE 8 compatibility is a concern you should use new Date().valueOf() at the cost of slightly diminished code readability.

Or if you want to use Date.now() but must be compatible with browsers which don't support it, you can place following code somewhere in your JavaScript files, which will add support for it.

if (!Date.now) {
    Date.now = function() {
        return new Date().getTime();
    }
}