This is an alternative way to deliver a string version of a date value. In this case, it is formatted as a Date literal and can then be used in an eval() function to assign another date.
If you run the example below, it should yield something resembling this:
Note that the date value is in milliseconds UTC time, and will vary, but you should see a very long number like that.
// Create a date object and display its source myObject = new Date(); document.write(myObject.toSource());