The once instance method, implemented in the Uize.Class base class module, has been improved with support for optional condition inversion.

As a convenience, the once method now supports condition inversion through an optional "!" (logical not) prefix that can be placed before the condition name.

EXAMPLE

myCollectionWidget.once (
  '!isEmpty',
  function () {
    // do something now that the collection is no longer empty
  }
);

In the above example, code is being registered to execute once the isEmpty condition becomes false. This is done by prefixing the "isEmpty" condition name with a "!" (bang / exclamation) character to indicate that the code should execute only once the collection is not empty (i.e. the value of the isEmpty state property becomes false). The condition inversion facility is convenient in situations like this where you wish to execute code only once a condition becomes unmet, rather than once the condition becomes met (which is the standard behavior for the once method).