LitElement bindings for @tanstack/query-core.

A tiny library which exposes the intuitive API of @tanstack/query, similarly to react-query et al.

Only the essentials are implemented for now.

Equivalents are exposed for

• QueryClientProvider
• useQueryClient
• useQuery
• useMutation

If you've ever used react-query the interface is familiar. lit-query exposes a few decorators to provide the query client to a component tree and to consume queries and mutations.

Create a query client and provide it to your component tree like so:

import { QueryClient } from "@tanstack/query-core";
import { provideQueryClient } from "lit-query";

@customElement("my-app")
export class MyApp extends LitElement {
  @provideQueryClient
  client = new QueryClient();

  render() {
    return html`...`;
  }
}

The QueryClient comes from the core library and manages its own query cache. Any component which wants to use queries/mutations needs to have access to it. This decorator uses context (similarly to React's context) to make the client available.

You use queries and mutations with the consumeQuery and consumeMutation property decorators. You use them on a property which will represent the state of the query. Like so:

@customElement("todos-list")
export class TodosApp extends LitElement {
  @consumeQuery(["todos"], () => fetch(`/api/todos`).then((res) => res.json()))
  query?: QueryObserverResult<{ todos: Todo[] }>;
  
  @consumeMutation({ mutationFn: (todo: Minimal<Todo>) => toggleTodo(todo) })
  toggleMutation?: Mutation<Todo, unknown, Partial<Todo> & { id: string }>;

  render() {
    return html`...`;
  }
}

In React, hooks are used in a shared scope where it is easy to call useQueryClient and access the client in a subsequent useMutation. A common use-case for this is setting query data with the result of a mutation.

In Lit things work differently, so instead, the QueryClient is always provided by lit-query as part of the mutation context.

Here's an example:

@consumeMutation({
  mutationFn: (todo: Minimal<Todo>) => toggleTodo(todo),
  onSuccess: (result, _vars, context) => {
    context?.client.setQueryData(
      ["todos"],
      produce<{ todos: Todo[] }>(({ todos }) => {
        const item = todos.find((item) => item.id === result.id);
        if (item) Object.assign(item, result);
      })
    );
  },
})
toggleMutation?: Mutation<Todo, unknown, Partial<Todo> & { id: string }>;

The decorators exposed by this library work by attaching Reactive Controllers to components.