5.11. Generating a Unique Number
You want to generate a unique number to append to a URL to prevent the browser from retrieving the asset from the local cache.
Use the number of milliseconds elapsed since January 1, 1970, as
Date( ).getTime( ).
Unique numbers are most commonly used to generate a unique URL (to prevent an asset from being retrieved from the local cache). That is, by appending a unique number to the end of a URL, it is unlike any previous URL; therefore, the browser obtains the data from the remote server instead of the local cache.
Assuming you need a unique number less frequently than once per
millisecond, the number of milliseconds returned by
).getTime( ) is essentially unique (at least during the
execution of your movie).
Note that you do not want to use the milliseconds of an existing
Date object because its time value
doesn’t automatically increase as your movie runs.
Instead, generate a new
Date object representing
“now” each time you need to extract
a unique number.
Here, we define our custom
method to encapsulate the code to generate the unique
number. By default, the method automatically generates a new value
each time it is called. However, if you pass it a
useCached parameter of
the method returns the same ID that it generated the last time it was
called. This can be useful if you want to create a single ID for a
movie and access it multiple times.
Math.getUniqueID = function (useCached) ...