Method getOptimisticResult

packages/query-core/src/queryObserver.ts:217–252

(
    options: DefaultedQueryObserverOptions<
      TQueryFnData,
      TError,
      TData,
      TQueryData,
      TQueryKey
    >,
  )

  }

  getOptimisticResult(
    options: DefaultedQueryObserverOptions<
      TQueryFnData,
      TError,
      TData,
      TQueryData,
      TQueryKey
    >,
  ): QueryObserverResult<TData, TError> {
    const query = this.#client.getQueryCache().build(this.#client, options)

    const result = this.createResult(query, options)

    if (!shallowEqualObjects(this.getCurrentResult(), result)) {
      // this assigns the optimistic result to the current Observer
      // because if the query function changes, useQuery will be performing
      // an effect where it would fetch again.
      // When the fetch finishes, we perform a deep data cloning in order
      // to reuse objects references. This deep data clone is performed against
      // the `observer.currentResult.data` property
      // When QueryKey changes, we refresh the query and get new `optimistic`
      // result, while we leave the `observer.currentResult`, so when new data
      // arrives, it finds the old `observer.currentResult` which is related
      // to the old QueryKey. Which means that currentResult and selectData are
      // out of sync already.
      // To solve this, we move the cursor of the currentResult every time
      // an observer reads an optimistic value.

      // When keeping the previous data, the result doesn't change until new
      // data arrives.
      this.#currentResult = result
      this.#currentResultOptions = this.options
      this.#currentResultState = this.#currentQuery.state
    }
    return result
  }

  getCurrentResult(): QueryObserverResult<TData, TError> {
    return this.#currentResult