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

👜 Callbag operator that combines consecutive values from the same source
https://github.com/staltz/callbag-scan

Last synced: about 2 months ago
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👜 Callbag operator that combines consecutive values from the same source

• Host: GitHub
• URL: https://github.com/staltz/callbag-scan
• Owner: staltz
• License: mit
• Created: 2018-01-23T21:39:22.000Z (over 6 years ago)
• Default Branch: master
• Last Pushed: 2021-12-28T12:44:17.000Z (over 2 years ago)
• Last Synced: 2024-07-20T04:04:51.153Z (2 months ago)
• Language: JavaScript
• Homepage:
• Size: 11.7 KB
• Stars: 6
• Watchers: 3
• Forks: 3
• Open Issues: 1
• Metadata Files:
  • Readme: readme.js
  • License: LICENSE

Awesome Lists containing this project

• awesome-callbags - scan

README

        
/**

 * callbag-scan

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

 *

 * Callbag operator that combines consecutive values from the same source.

 * It's essentially like array `.reduce`, but delivers a new accumulated value

 * for each value from the callbag source. Works on either pullable or

 * listenable sources.

 *

 * `npm install callbag-scan`

 *

 * Example:

 *

 *     const fromIter = require('callbag-from-iter');

 *     const forEach = require('callbag-for-each');

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

 *

 *     const iterSource = fromIter([1,2,3,4,5]);

 *     const scanned = scan((prev, x) => prev + x, 0)(iterSource);

 *

 *     forEach(x => console.log(x))(scanned);    // 1

 *                                               // 3

 *                                               // 6

 *                                               // 10

 *                                               // 15

 */

function scan(reducer, seed) {

  let hasAcc = arguments.length === 2;

  return source => (start, sink) => {

    if (start !== 0) return;

    let acc = seed;

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

      if (t === 1) {

        acc = hasAcc ? reducer(acc, d) : ((hasAcc = true), d);

        sink(1, acc);

      } else sink(t, d);

    });

  };

}

module.exports = scan;