Method load

src/index.js:74–113

* Loads a key, returning a `Promise` for the value represented by that key.

(key: K)

   * Loads a key, returning a `Promise` for the value represented by that key.
   */
  load(key: K): Promise<V> {
    if (key === null || key === undefined) {
      throw new TypeError(
        'The loader.load() function must be called with a value, ' +
          `but got: ${String(key)}.`,
      );
    }

    const batch = getCurrentBatch(this);
    const cacheMap = this._cacheMap;
    let cacheKey: ?C;

    // If caching and there is a cache-hit, return cached Promise.
    if (cacheMap) {
      cacheKey = this._cacheKeyFn(key);
      const cachedPromise = cacheMap.get(cacheKey);
      if (cachedPromise) {
        const cacheHits = batch.cacheHits || (batch.cacheHits = []);
        return new Promise(resolve => {
          cacheHits.push(() => {
            resolve(cachedPromise);
          });
        });
      }
    }

    // Otherwise, produce a new Promise for this key, and enqueue it to be
    // dispatched along with the current batch.
    batch.keys.push(key);
    const promise = new Promise((resolve, reject) => {
      batch.callbacks.push({ resolve, reject });
    });

    // If caching, cache this promise.
    if (cacheMap) {
      cacheMap.set((cacheKey: any), promise);
    }

    return promise;
  }

  /**
   * Loads multiple keys, promising an array of values: