addHasValuesListener

The addHasValuesListener method registers a listener function with the Store that will be called when Values as a whole are added to or removed from the Store.

addHasValuesListener(
  listener: HasValuesListener,
  mutator?: boolean,
): Id

The provided listener is a HasValuesListener function, and will be called with a reference to the Store. It is also given a flag to indicate whether Values now exist (having not done previously), or do not (having done so previously).

Use the optional mutator parameter to indicate that there is code in the listener that will mutate Store data. If set to false (or omitted), such mutations will be silently ignored. All relevant mutator listeners (with this flag set to true) are called before any non-mutator listeners (since the latter may become relevant due to changes made in the former). The changes made by mutator listeners do not fire other mutating listeners, though they will fire non-mutator listeners.

const store = createStore().setValues({open: true, employees: 3});
const listenerId = store.addHasValuesListener((store, hasValues) => {
  console.log('Values ' + (hasValues ? 'added' : 'removed'));
});

store.delValues();
// -> 'Values removed'

store.setValue('employees', 4);
// -> 'Values added'

store.delListener(listenerId);

const store = createStore();
const listenerId = store.addHasValuesListener(
  (store, hasValues) => store.setValue('hasValues', hasValues),
  true,
);

store.setValue('employees', 4);
console.log(store.getValues());
// -> {employees: 4, hasValues: true}

store.delListener(listenerId);