`addHasRowListener`

The addHasRowListener method registers a listener function with the Store that will be called when a Row is added to or removed from the Store.

addHasRowListener(
  tableId: IdOrNull,
  rowId: IdOrNull,
  listener: HasRowListener<Store>,
  mutator?: boolean,
): string

	Type	Description
`tableId`	`IdOrNull`	The `Id` of the `Table` to listen to, or `null` as a wildcard.
`rowId`	`IdOrNull`	The `Id` of the `Row` to listen to, or `null` as a wildcard.
`listener`	`HasRowListener<Store>`	The function that will be called whenever the matching `Row` is added or removed.
`mutator?`	`boolean`	An optional boolean that indicates that the listener mutates `Store` data.
returns	`string`	A unique `Id` for the listener that can later be used to call it explicitly, or to remove it.

The provided listener is a HasRowListener function, and will be called with a reference to the Store, the Id of the Table that changed, and the Id of the Row that changed. It is also given a flag to indicate whether the Row now exists (having not done previously), or does not (having done so previously).

You can either listen to a single Row being added or removed (by specifying the Table Id and Row Id, as the method's first two parameters) or changes to any Row (by providing null wildcards).

Both, either, or neither of the tableId and rowId parameters can be wildcarded with null. You can listen to a specific Row in a specific Table, any Row in a specific Table, a specific Row in any Table, or any Row in any Table.

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.

Examples

This example registers a listener that responds to a specific Row being added or removed.

import {createStore} from 'tinybase';

const store = createStore().setTables({
  pets: {fido: {species: 'dog', color: 'brown'}},
});
const listenerId = store.addHasRowListener(
  'pets',
  'fido',
  (store, tableId, rowId, hasRow) => {
    console.log(
      'fido row in pets table ' + (hasRow ? 'added' : 'removed'),
    );
  },
);

store.delRow('pets', 'fido');
// -> 'fido row in pets table removed'

store.setRow('pets', 'fido', {species: 'dog', color: 'brown'});
// -> 'fido row in pets table added'

store.delListener(listenerId);

This example registers a listener that responds to any Row being added or removed.

import {createStore} from 'tinybase';

const store = createStore().setTables({
  pets: {fido: {species: 'dog', color: 'brown'}},
});
const listenerId = store.addHasRowListener(
  null,
  null,
  (store, tableId, rowId, hasRow) => {
    console.log(
      `${rowId} row in ${tableId} table ` + (hasRow ? 'added' : 'removed'),
    );
  },
);

store.delRow('pets', 'fido');
// -> 'fido row in pets table removed'
store.setTable('species', {dog: {price: 5}});
// -> 'dog row in species table added'

store.delListener(listenerId);

This example registers a listener that responds to a specific Row being added or removed, and which also mutates the Store itself.

import {createStore} from 'tinybase';

const store = createStore().setTables({
  pets: {fido: {species: 'dog', color: 'brown'}},
});
const listenerId = store.addHasRowListener(
  'pets',
  'fido',
  (store, tableId, rowId) =>
    store.setCell('meta', 'update', `${tableId}_${rowId}`, true),
  true,
);

store.delRow('pets', 'fido');
console.log(store.getTable('meta'));
// -> {update: {pets_fido: true}}

store.delListener(listenerId);

Since

v4.4.0