count of desktops only returns 1

Any idea why the following script would only return 1, when I clearly have more than one Desktop open?

tell application "System Events"
    set n to count of desktops
    display alert n
end tell

I have even tried it with JAX JavaScript and also get 1.

Note: For reference I am using El Capitan (MBP Mid 2012)

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Solution 1:

'desktops' are 'monitors' not Spaces.
There's no programmatic way to count Spaces, short of using the GUI, which is very hit & miss.