@async-generators/bundle

bundle

bundle items until a condition is met and yield as an iterable

Usage

package requires a system that supports async-iteration, either natively or via down-compiling

Install

npm install @async-generators/bundle --save
yarn add @async-generators/bundle

This package's main entry points to a commonjs distribution.

Additionally, the module entry points to a es2015 distribution, which can be used by build systems, such as webpack, to directly use es2015 modules.

Api

bundle(source, condition)

bundle() iterates source and stores each item in an array while a condition is true, after which the bundle array is yielded (as an array). If the source completes any remaining non-empty bundled array is yielded.

• when condition is a number, items are stored until the array contains condition number of items.
• when condition is a function, source items are stored in the current bundle if condition(item, buffer) === true.
• when condition(item, buffer) === false the current bundle is yielded (sans item) and a new bundle is created containing the latest item.

Example 1 - fixed size

example.js

const bundle = require('@async-generators/bundle').default;

async function main() {
  let source = async function* () {
    yield 1;
    yield 2;
    yield 3;
    yield 4;
    yield 5;
  }
  for await (let item of bundle(source(), 2)) {
    console.log(items);
  }
}

main();

Execute with the latest node.js:

node --harmony-async-iteration example.js

output:

[ 1, 2 ]
[ 3, 4 ]
[ 5 ]

Example 2 - throttle

example.js

const bundle = require('@async-generators/bundle').default;
async function delay(duration) {
  return new Promise(r => setTimeout(r, duration));
}

function throttle(period) {
  let next;
  return function () {
    let start = function(){
      next = false;
      console.log("started timeout", period);
      setTimeout(function () { 
        next = true; 
        console.log("timed-out");
      }, period);
    }

    if (next === undefined) {
      start();
      return true;
    }
    if (next) {      
      start();
      return false;
    }
    if (next) {      
      next = undefined;
      return false;
    }
    return true;
  }
}

async function main() {
  let source = async function* () {
    for (let i = 0; i < 10; i++) {   
      console.log("source yield", i);   
      yield i;      
      await delay(100);     
    }
  }

  for await (let items of bundle(source(), throttle(350))) {
    console.log("bundle yield", items);
  }
}

main();

Execute with the latest node.js:

node --harmony-async-iteration example.js

output:

source yield 0
started timeout 350
source yield 1
source yield 2
source yield 3
timed-out
source yield 4
started timeout 350
bundle yield [ 0, 1, 2, 3 ]
source yield 5
source yield 6
source yield 7
timed-out
source yield 8
started timeout 350
bundle yield [ 4, 5, 6, 7 ]
source yield 9
bundle yield [ 8, 9 ]
timed-out

Typescript

This library is fully typed and can be imported using:

import bundle from '@async-generators/bundle');

It is also possible to directly execute your properly configured typescript with ts-node:

ts-node --harmony_async_iteration example.ts