https://github.com/staltz/callbag-combine

👜 Callbag factory that combines data from multiple callbag sources
https://github.com/staltz/callbag-combine

Last synced: about 2 months ago
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👜 Callbag factory that combines data from multiple callbag sources

• Host: GitHub
• URL: https://github.com/staltz/callbag-combine
• Owner: staltz
• License: mit
• Created: 2018-01-23T21:13:42.000Z (over 6 years ago)
• Default Branch: master
• Last Pushed: 2021-12-25T10:20:56.000Z (over 2 years ago)
• Last Synced: 2024-07-23T06:48:26.950Z (about 2 months ago)
• Language: JavaScript
• Homepage:
• Size: 16.6 KB
• Stars: 7
• Watchers: 3
• Forks: 3
• Open Issues: 0
• Metadata Files:
  • Readme: readme.js
  • License: LICENSE

Awesome Lists containing this project

• awesome-callbags - combine

README

        
/**

 * callbag-combine

 * ---------------

 *

 * Callbag factory that combines the latest data points from multiple (2 or

 * more) callbag sources. It delivers those latest values as an array. Works

 * with both pullable and listenable sources.

 *

 * `npm install callbag-combine`

 *

 * Example:

 *

 *     const interval = require('callbag-interval');

 *     const observe = require('callbag-observe');

 *     const combine = require('callbag-combine');

 *

 *     const source = combine(interval(100), interval(350));

 *

 *     observe(x => console.log(x))(source); // [2,0]

 *                                           // [3,0]

 *                                           // [4,0]

 *                                           // [5,0]

 *                                           // [6,0]

 *                                           // [6,1]

 *                                           // [7,1]

 *                                           // [8,1]

 *                                           // ...

 */

const EMPTY = {};

const combine = (...sources) => (start, sink) => {

  if (start !== 0) return;

  const n = sources.length;

  if (n === 0) {

    sink(0, () => {});

    sink(1, []);

    sink(2);

    return;

  }

  let Ns = n; // start counter

  let Nd = n; // data counter

  let Ne = n; // end counter

  const vals = new Array(n);

  const sourceTalkbacks = new Array(n);

  const talkback = (t, d) => {

    if (t === 0) return;

    for (let i = 0; i < n; i++) sourceTalkbacks[i](t, d);

  };

  sources.forEach((source, i) => {

    vals[i] = EMPTY;

    source(0, (t, d) => {

      if (t === 0) {

        sourceTalkbacks[i] = d;

        if (--Ns === 0) sink(0, talkback);

      } else if (t === 1) {

        const _Nd = !Nd ? 0 : vals[i] === EMPTY ? --Nd : Nd;

        vals[i] = d;

        if (_Nd === 0) {

          const arr = new Array(n);

          for (let j = 0; j < n; ++j) arr[j] = vals[j];

          sink(1, arr);

        }

      } else if (t === 2) {

        if (--Ne === 0) sink(2);

      } else {

        sink(t, d);

      }

    });

  });

};

module.exports = combine;