first commit

.gitignore

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+.DS_Store
+node_modules
+package-lock.json
+dist

README.md

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+# async-iterator-talk
+
+These are the slides for a talk on async iterators at VanJS on February 27th, 2019.

assets/about.js

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+module.exports = {
+  "name": "Stephen Belanger",
+  "github": "https://github.com/qard",
+  "twitter": "https://twitter.com/stephenbelanger",
+  "work": "Node.js APM Agent Developer at Elastic"
+}

assets/async-iterator-pipe.js

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+async function pipeStream (iterator, stream) {
+  for await (let chunk of iterator) {
+    stream.write(chunk)
+  }
+  stream.end()
+}
+
+function pipeDirect (source, target) {
+  if (target.write && target.end) {
+    pipeStream(source, target)
+    return target
+  } else if (typeof target === 'function') {
+    return target(source)
+  } else {
+    throw new Error('Unrecognized target type')
+  }
+}
+
+function pipe (source, ...transforms) {
+  return transforms.reduce(pipeDirect, source)
+}
+
+module.exports = pipe

assets/batching.js

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+function timeout (ms) {
+  return new Promise(done => setTimeout(done, ms))
+}
+
+async function* numbers () {
+  let n = 0
+  while (true) {
+    await timeout(10)
+    yield n++
+  }
+}
+
+async function* take (iterator, n) {
+  while (n-- !== 0) {
+    const item = await iterator.next()
+    if (!item.done) yield item.value
+  }
+}
+
+async function toArray (iterator) {
+  const items = []
+  for await (let item of iterator) {
+    items.push(item)
+  }
+  return items
+}
+
+async function* batch (iterator, size) {
+  while (true) {
+    const page = take(iterator, size)
+    const slice = await toArray(page)
+    if (!slice.length) break
+    yield slice
+  }
+}
+
+function sum (items) {
+  return items.reduce((m, v) => m + v, 0)
+}
+
+const batches = batch(numbers(), 8)
+for await (let slice of take(batches, 10)) {
+  console.log(sum(slice))
+}

assets/custom-async-iterator.js

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+function interval (ms) {
+  const iterator = {
+    async next () {
+      await timeout(ms)
+      return {
+        value: Date.now(),
+        done: false
+      }
+    }
+  }
+
+  const generator = {
+    [Symbol.asyncIterator] () {
+      return iterator
+    }
+  }
+
+  return generator
+}

assets/http-iterator.js

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+const Channel = require('channel-surfer')
+
+module.exports = function httpIterator (server) {
+  const channel = new Channel()
+
+  server.on('request', (request, response) => {
+    channel.give({ request, response })
+  })
+
+  server.on('close', () => {
+    channel.close()
+  })
+
+  return channel
+}

assets/http-server.js

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+const http = require('http')
+const httpIterator = require('http-iterator')
+
+const server = http.createServer()
+server.listen(3000)
+
+const requests = httpIterator(server)
+for await (let { response } of requests) {
+  response.end('hello world')
+}

assets/interval.js

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+function timeout (ms) {
+  return new Promise(done => {
+    setTimeout(done, ms)
+  })
+}
+
+async function* interval (ms) {
+  while (true) {
+    await timeout(ms)
+    yield Date.now()
+  }
+}
+
+for await (let time of interval(1000)) {
+  console.log(time)
+}

assets/iterable-http-requests.js

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+const toIter = require('http-iterator')
+const http = require('http')
+
+const server = http.createServer()
+server.listen(3000)
+
+for await (let { response } of toIter(server)) {
+  response.end('hello world')
+}

assets/pagination.js

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+const pageList = [
+  {
+    items: [
+      { name: 'first' },
+      { name: 'second' }
+    ]
+  },
+  {
+    items: [
+      { name: 'third' },
+      { name: 'fourth' }
+    ]
+  }
+]
+
+async function loadPage (n) {
+  await timeout(100) // Simulate async
+  return pageList[n]
+}
+
+async function* getPages () {
+  let n = 0
+  let page
+
+  while ((page = await loadPage(n++))) {
+    yield page
+  }
+}
+
+async function* pagesToItems (pages) {
+  for await (let page of pages) {
+    for (let item of page.items) {
+      yield item
+    }
+  }
+}
+
+const pages = getPages()
+const items = pagesToItems(pages)
+
+for await (let item of items) {
+  console.log(item.name)
+}

assets/stream-line-split.js

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+const pipe = require('async-iterator-pipe')
+
+async function* lineSplit (iterator) {
+  let buffer = ''
+  for await (let chunk of iterator) {
+    buffer += chunk.toString()
+    let position = buffer.indexOf('\n')
+    while (position >= 0) {
+      yield buffer.slice(0, position)
+      buffer = buffer.slice(position + 1)
+      position = buffer.indexOf('\n')
+    }
+  }
+}
+
+async function* csv (iterator) {
+  let keys
+  for await (let line of iterator) {
+    const values = line.split(',')
+    if (!keys) {
+      keys = values
+    } else {
+      const data = {}
+      for (let i = 0; i < values.length; i++) {
+        data[keys[i]] = values[i]
+      }
+      yield data
+    }
+  }
+}
+
+async function* toJSON (iterator) {
+  for await (let item of iterator) {
+    yield JSON.stringify(item)
+  }
+}
+
+const fs = require('fs')
+pipe(
+  fs.createReadStream('./assets/test.csv'),
+  lineSplit,
+  csv,
+  toJSON,
+  process.stdout
+)

assets/stream-transforms.js

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+const pipe = require('async-iterator-pipe')
+const zlib = require('zlib')
+
+async function* upper (iterator) {
+  for await (let item of iterator) {
+    yield item.toString().toUpperCase()
+  }
+}
+
+pipe(
+  process.stdin,
+  zlib.createGunzip(),
+  upper,
+  zlib.createGzip(),
+  process.stdout
+)

assets/streams.js

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+async function concat (stream) {
+  const chunks = []
+  for await (let chunk of stream) {
+    chunks.push(chunk)
+  }
+  return Buffer.concat(chunks)
+}
+
+const body = await concat(
+  fs.createReadStream(__filename)
+)

assets/test.csv

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+key,value
+foo,bar
+baz,buz

code-surfer.js

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+import React from 'react'
+import { CodeSurfer } from "mdx-deck-code-surfer"
+import vsDarkPlus from "prism-react-renderer/themes/vsDarkPlus"
+
+const CustomCodeSurfer = ({ title, code, steps }) => (
+  <CodeSurfer
+    title={title}
+    code={code}
+    lang="javascript"
+    showNumbers={false}
+    theme={vsDarkPlus}
+    steps={steps}
+  />
+)
+
+export default CustomCodeSurfer

now.json

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+{
+  "version": 2,
+  "name": "async-iterators-a-new-future-for-streams",
+  "alias": "async-iterators-talk.now.sh",
+  "builds": [
+    {
+      "src": "package.json",
+      "use": "@now/static-build"
+    }
+  ]
+}

package.json

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+{
+  "name": "async-iterator-talk",
+  "version": "1.0.0",
+  "description": "VanJS talk about async iterators and streams",
+  "scripts": {
+    "start": "mdx-deck slides.mdx",
+    "build": "npm run build:presentation && npm run build:assets",
+    "build:presentation": "mdx-deck build slides.mdx --no-html",
+    "build:assets": "cp -r assets dist/",
+    "now-build": "npm run build",
+    "deploy": "now"
+  },
+  "author": "Stephen Belanger <[email protected]> (https://github.com/qard)",
+  "license": "MIT",
+  "devDependencies": {
+    "mdx-deck": "^1.8.2",
+    "mdx-deck-code-surfer": "^0.5.5",
+    "now": "^13.1.3",
+    "prism-react-renderer": "^0.1.5",
+    "raw-loader": "^1.0.0"
+  }
+}