What does !1 and !0 mean in Javascript? [duplicate]

Possible Duplicate:
return !1 in javascript

In a JavaScript file I had to read today, there was a line where a variable was declared like a factorial, like this :

var myVariable = !1;

and then something similar was used as parameter in a function like this :

return variable.myFunction(!0);

Can anyone explain me what the exclamation mark means in this context and eventually, why this is generally used for (benefits) ?

Thank you in advance !

The ! is the boolean NOT operator.

NOT (!): toggles a statement from true to false or from false to true.

!0 = true
!1 = false

This is a brilliant introduction to boolean operators and their use in javascript.