batchloader/lib/mappedbatchloader.js

BatchLoader is a utility for data fetching layer to reduce requests via batching written in TypeScript. Inspired by Facebook's DataLoader

export class MappedBatchLoader {
    constructor(loader, mapFn) {
        this.loader = loader;
        this.mapFn = mapFn;
    }
    load(key) {
        return this.loader.load(key).then((value) => this.mapFn(value, key));
    }
    loadMany(keys) {
        return this.loader.loadMany(keys).then((values) => {
            let hasPromise = false;
            const results = [];
            const len = values.length;
            for (let i = 0; i < len; i += 1) {
                const res = this.mapFn(values[i], keys[i]);
                results.push(res);
                hasPromise =
                    hasPromise ||
                        (res != null && typeof res.then === 'function');
            }
            return hasPromise ? Promise.all(results) : results;
        });
    }
    mapLoader(mapFn) {
        return new MappedBatchLoader(this, mapFn);
    }
}
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