Package Exports

promax

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Readme

promax

Another promise limiter (adding concurrency to promises). This library uses rxjs to control concurrency, it also adds a little bit of extra functionality around how you get the results.

Setup Instructions

To install this package, run,

npm install --save promax

Usage Instructions

Once it's installed, you can use Promax to run your promises with a specified concurrency value. Pretend we had the following promise function:

function createPromiseFunction(returns = null, timeout = 0) {
  return new Promise(resolve => {
    setTimeout(() => {
      resolve(returns);
    }, timeout);
  });
}

Our code with Promax could be used in many ways:

import { Promax } from 'promax';

async function run() {
    const limit = 2;
    const expectedValues = [1, 2, 3];
    const promax = Promax.create(limit).add(
        expectedValues.map(ev => () => createPromiseFunction(ev))
    );
    const results = await promax.run();
    // In this case, results == expectedValues
    
    const resultMap = promax.getResultMap();
    /**
     * This would return:
     * {
     *    valid: [1, 2, 3],
     *    error: []
     * }
     */
}

NOTE: In this case, we didn't change the settings at the start so if a promise is rejected, it'll throw and end the call.

What if we don't want it do throw?

import { Promax } from 'promax';

async function run() {
    const limit = 2;
    const expectedValues = [1, 2, 3];
    const promax = Promax.create(limit, { throws: false }).add(
        expectedValues.map(ev => () => createPromiseFunction(ev))
    );
    // ... same as previous example
}

When it doesn't throw, it wraps errored results in an ErrorResult instance. Using insanceof ErrorResult will tell you whether or not there was an error in your array of results. Let's assume we have the following function,

function createFailedPromiseFunction(returns = 0, timeout = 0) {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            reject(returns);
        }, timeout);
    });
}

Then we may get the following,

import { Promax } from 'promax';

async function run() {
    const limit = 2;
    const promax = Promax.create(limit, { throws: false }).add([
        () => createPromiseFunction(1),
        () => createFailedPromiseFunction(2),
        () => createPromiseFunction(3),
    ]);
    const results = await promax.run();
    /**
     * Now we would have the following
     * results = [
     *    1,
     *    ErrorResult,
     *    2
     *  ]
     *
     * So:
     * results[0] === 1
     * results[1] instanceof ErrorResult
     * results[1].data === 2
     * results[2] === 3
     */
    
    const resultMap = promax.getResultMap();
    /**
     * This would return:
     * {
     *    valid: [1, 3],
     *    error: [ErrorResult]
     * }
     */
}

IMPORTANT: If you don't need the functionality above, you can chain everything into one call:

import { Promax } from 'promax';

async function run() {
    const limit = 2;
    const expectedValues = [1, 2, 3];
    const results = Promax.create(limit).add(
        expectedValues.map(ev => () => createPromiseFunction(ev))
    ).run();
}

And you can send in the result map by reference:

import { Promax } from 'promax';

async function run() {
    const limit = 2;
    const expectedValues = [1, 2, 3];
    const resultMap = { valid: [], error: [] };
    const results = Promax.create(limit)
        .setResultMapOutput(resultMap)
        .add(
            expectedValues.map(ev => () => createPromiseFunction(ev))
        ).run();
    /**
     * In this case:
     *
     * results = [1, 2, 3]
     * resultMap = {
     *    valid: [1, 2, 3],
     *    error: []
     * }
     */

}