`useHasValue`

The useHasValue hook returns a boolean indicating whether a given Value exists in the Store, and registers a listener so that any changes to that result will cause a re-render.

useHasValue(
  valueId: string,
  storeOrStoreId?: StoreOrStoreId,
): boolean

Type Description

	Type	Description
`valueId`	`string`	The `Id` of the `Value` in the `Store`.
`storeOrStoreId?`	`StoreOrStoreId`	The `Store` to be accessed: omit for the default context `Store`, provide an `Id` for a named context `Store`, or provide an explicit reference.
returns	`boolean`	Whether a `Value` with that `Id` exists in the `Store`.

valueId

string

The Id of the Value in the Store.

storeOrStoreId?

StoreOrStoreId

The Store to be accessed: omit for the default context Store, provide an Id for a named context Store, or provide an explicit reference.

returns

boolean

Whether a Value with that Id exists in the Store.

A Provider component is used to wrap part of an application in a context, and it can contain a default Store or a set of Store objects named by Id. The useHasValue hook lets you indicate which Store to get data for: omit the optional parameter for the default context Store, provide an Id for a named context Store, or provide a Store explicitly by reference.

When first rendered, this hook will create a listener so that changes to the Value will cause a re-render. When the component containing this hook is unmounted, the listener will be automatically removed.

Examples

This example creates a Store outside the application, which is used in the useHasValue hook by reference. A change to the data in the Store re-renders the component.

import React from 'react';
import {createRoot} from 'react-dom/client';
import {createStore} from 'tinybase';
import {useHasValue} from 'tinybase/ui-react';

const store = createStore().setValue('open', true);
const App = () => (
  <span>{JSON.stringify(useHasValue('employees', store))}</span>
);

const app = document.createElement('div');
const root = createRoot(app);
root.render(<App />);
console.log(app.innerHTML);
// -> '<span>false</span>'

store.setValue('employees', 3);
console.log(app.innerHTML);
// -> '<span>true</span>'

This example creates a Provider context into which a default Store is provided. A component within it then uses the useHasValue hook.

import {Provider, useHasValue} from 'tinybase/ui-react';
import React from 'react';
import {createRoot} from 'react-dom/client';
import {createStore} from 'tinybase';

const App = ({store}) => (
  <Provider store={store}>
    <Pane />
  </Provider>
);
const Pane = () => <span>{JSON.stringify(useHasValue('employees'))}</span>;

const store = createStore().setValue('open', true);
const app = document.createElement('div');
createRoot(app).render(<App store={store} />);
console.log(app.innerHTML);
// -> '<span>false</span>'

This example creates a Provider context into which a Store is provided, named by Id. A component within it then uses the useHasValue hook.

import {Provider, useHasValue} from 'tinybase/ui-react';
import React from 'react';
import {createRoot} from 'react-dom/client';
import {createStore} from 'tinybase';

const App = ({store}) => (
  <Provider storesById={{petStore: store}}>
    <Pane />
  </Provider>
);
const Pane = () => (
  <span>{JSON.stringify(useHasValue('employees', 'petStore'))}</span>
);

const store = createStore().setValue('open', true);
const app = document.createElement('div');
createRoot(app).render(<App store={store} />);
console.log(app.innerHTML);
// -> '<span>false</span>'

Since

v4.4.0