Sequential promise-based batches for JavaScript or TypeScript

index.ts

/**
 * Task is just an async function that accepts no arguments and returns a promise with result
 * Example: `async () => new Promise(...)`
 */
export const sequentialBatches = async <T>(tasks: (() => Promise<T>)[], maxConcurrency = 100): Promise<T[]> => {
    const batches = tasks.reduce((res, task, index) => {
        const batchIndex = Math.floor(index / maxConcurrency);
        res[batchIndex] = res[batchIndex] || [];
        res[batchIndex].push(task);
        return res;
    }, []);

    let res = [];

    console.log('Batch processing of', tasks.length, 'tasks');

    for (const batch of batches) {
        console.log('Batch', batches.indexOf(batch) + 1, 'of', batches.length, 'this batch length', batch.length);
        res = res.concat(await Promise.all(batch.map(task => task())));
    }

    console.log('Batch processing done', res.length, 'tasks finished');

    return res;
};

// usage
  
const ids = [1,2,3,4,5,6,7,8,9,10];
  
const getSomething = sequentialBatches(ids.map(id => async () => fetch(`http://example.com/${id})), 5);
  
//TODO Make an NPM lib