Gleb Bahmutov PRO
JavaScript ninja, image processing expert, software quality fanatic
Modern JavaScript
#boscc
Gleb Bahmutov, PhD
Boston Code Camp 2018
undefined is not a function
About: @bahmutov
- Startups / medium size / MathWorks
- VP of Eng at Cypress.io
- Computer vision background (C/C++/C#)
CoffeeScript then JavaScript
- Hundreds of OSS projects
- Hundreds of blog posts
- 50 meetup and conference decks
About: @bahmutov
A software product
User
Data
Servers
UI
C++ / C# Java
SilverLight
Java
A software product
User
Data
Servers
UI
JavaScript
JavaScript
Desktop
Deploy
Mobile app
We are going to cover:
- Where is JavaScript?
- JavaScript versions
- Main tools
JavaScript around us
-
Browser
-
Server
-
Desktop
-
Mobile
-
Gray areas:
-
IoT, robots, code snippets, build scripts, sw
-
<div onclick="alert('hi')">Click me</div>Modern JavaScript
in the Browser
<script src="app.js"></script>
<div id="app" />Single Page Applications (SPA)
React, Angular, Vue, Ember
Modern JavaScript
in the Browser
No longer relevant
JScript
VBScript
Dart
Flash
Silverlight
Java
Replacing mobile applications
Modern JavaScript
Browser/mobile
Two choices
Progressive Web App
I don't want to download 200MB app to read tweets
I can't afford to download 200MB app to read tweets
me
billions of people
Progressive Web Apps
- Visit URL in the browser
- Save on desktop
- Acts like an app:
- fast, offline, notifications
2nd: ReactNative
Code Web App convert to Native app
JS in the Browser: 4 places
Server
browser
Web Workers
ServiceWorker
(JavaScript)
Transforms
the response
Transforms
the request
DevTools
JavaScript vs Images
Most of the pages are images
But browsers choke on JS
Website is so slow!
Solution: put your JavaScript into images 🤔
node sever.js -p 3000Modern JavaScript
on Server
const http = require('http')
const hostname = '127.0.0.1'
const port = 3000
const server = http.createServer((req, res) => {
res.statusCode = 200
res.setHeader('Content-Type', 'text/plain')
res.end('Hello World\n')
})
server.listen(port, hostname, () => {
console.log(`Server running at
http://${hostname}:${port}/`)
})
Node Adoption: Everyone
Modern JavaScript
on Desktop
Build cross platform desktop apps with JavaScript, HTML, and CSS
Cypress.io E2E Test Runner
| Platform | CI | Output Binary |
|---|---|---|
| Darwin | Buildkite | Electron |
| Linux | CircleCI | Electron |
| Windows | AppVeyor | Electron |
Qt, Java, ... Node 👍
Cypress GUI is a web app itself running as Electron application
Shell scripts ➡ Nodejs scripts
if [ -d "foo" ] then:
cp -r foo bar
ficonst shell = require('shelljs')
if (fs.existsSync('foo')) {
shell.cp('-r', 'foo', 'bar')
}Works (Linux)
Mostly works (Darwin)
🔥 (Windows)
Just works!
All our build scripts are Nodejs files
I don't want to learn your cryptic script commands
-
Where is JavaScript?
-
Browser, server, mobile, shell scripts
-
- JavaScript versions
- Main tools
Modern JavaScript
Let's look at the JavaScript language
Modern JavaScript
- 1996: Netscape asks Ecma to make a "standard" JavaScript specifications
- 1997 Ecma publishes EcmaScript standard
Modern JavaScript
EcmaScript (ES) = standard
JavaScript = implementation
* "JavaScript" is a trademark of Oracle Co
*
Modern JavaScript
- June 2011: EcmaScript 5.1 (ES5)
All modern browsers
Modern JavaScript
- June 2011: EcmaScript 5.1 (ES5)
var x = 'foo'
var y = 42
function add(a, b) {
return a + b
}
add(x, y)
// EcmaScript has no input / output ⚠️Modern JavaScript
- June 2015: EcmaScript 2015 (ES6)
const x = 'foo'
[1, 2, 3].map(x => x + x)
console.log(`x = ${x}`)
// and lots of other things...Modern JavaScript
- June 2016: EcmaScript 2016
[1, 2, 3].includes(2) // true
2 ** 3 // 8Modern JavaScript
- June 2017: EcmaScript 2017
async function userName () {
try {
const user = await fetch()
return user.name
} catch (err) {
// deal with error
}
}Modern JavaScript
- June 2015: EcmaScript 2015 (ES6)
- June 2016: EcmaScript 2016 (ES7)
- June 2017: EcmaScript 2017
- June 2018: ...
How an idea becomes an EcmaScript feature
Anyone can propose a new feature
How an idea becomes an EcmaScript feature
I want JavaScript to have X
Stage 0
an idea is born
How an idea becomes an EcmaScript feature
Discussion, demos, polyfills
Feature gets a "champion"
Stage 1: proposal
How an idea becomes an EcmaScript feature
TC39 committee: about 25 members
Mozilla, Google, Apple, Intel, universities
Stage 1: proposal
How an idea becomes an EcmaScript feature
Draft and precise spec language is being developed
Stage 2: draft
How an idea becomes an EcmaScript feature
All semantics, syntax and API are completed described
Stage 3: candidate
How an idea becomes an EcmaScript feature
Feature has tests
Two reference implementations
Stage 4: finished
How an idea becomes an EcmaScript feature
Stage 4 features as of March
become part of the standard published in June
What does a browser support?
try {
eval('2 ** 8')
} catch () {
// ** is not supported
}
// ** is ✅What does a browser support?
- Evergreen browsers are 100% ES2015/2016/2017 compatible
*
* except for (maybe) ES6 modules
What does a browser support?
- Mobile browsers really patchy
1: Adding polyfills
Detect and polyfill only what's missing with modernizr.com
<script src="polyfills.js"></script>
<script>
[1, 2, 3].includes(2) // works now
</script>1: Adding polyfills
Does not work with every feature
<script src="polyfills.js"></script>
<script>
2 ** 3
// SyntaxError
</script>2: Transpiling
Rewrite code to older standard
2 ** 3 // app.jsbabel app.jsMath.pow(2, 3)ES2016
ES5
* not every feature can be transpiled
*
Talk progress
- Where is JavaScript?
- JavaScript versions
- Main tools
NPM Registry
aka OSS heaven
source: http://www.modulecounts.com
source: https://npms.io
Creating your own module
$ mkdir my-app
$ cd my-app
$ git init$ npm init -y$ npm publish$ npm init -y
Wrote to my-app/package.json
{
"name": "my-app",
"version": "1.0.0",
"description": "",
"main": "index.js",
"scripts": {
"test": "exit 1"
},
"keywords": [],
"author": "",
"license": "ISC"
}$ yo node-bahmutov
{
"name": "stop-build",
"version": "0.0.0-development",
"description": "Exits with non-zero code if there are modified Git files",
"author": "Gleb Bahmutov <gleb.bahmutov@gmail.com>",
"bugs": "https://github.com/bahmutov/stop-build/issues",
"config": {
"next-update": {
"commands": {
"pre-git": "./.git/hooks/pre-commit"
}
},
"pre-git": {
"commit-msg": "simple",
"pre-commit": [
"npm run pretest",
"npm run deps",
"npm run ban",
"git add ."
],
"pre-push": [
"npm test",
"npm run secure",
"npm run license",
"npm run ban -- --all",
"npm run size"
],
"post-commit": [],
"post-merge": []
}
},
"engines": {
"node": ">=6"
},
"files": [
"src/*.js",
"!src/*-spec.js"
],
"bin": {
"stop-build": "src/index.js"
},
"homepage": "https://github.com/bahmutov/stop-build#readme",
"keywords": [
"build",
"ci",
"exit",
"git",
"utility"
], "license": "MIT",
"main": "src/",
"publishConfig": {
"registry": "http://registry.npmjs.org/"
},
"repository": {
"type": "git",
"url": "https://github.com/bahmutov/stop-build.git"
},
"scripts": {
"ban": "ban",
"deps": "deps-ok",
"issues": "git-issues",
"license": "license-checker --production --onlyunknown --csv",
"pretty": "prettier-standard 'src/*.js'",
"prelint": "npm run pretty",
"lint": "standard --verbose --fix src/*.js",
"pretest": "npm run lint",
"secure": "nsp check",
"size": "t=\"$(npm pack .)\"; wc -c \"${t}\"; tar tvf \"${t}\"; rm \"${t}\";",
"test": "npm run unit",
"unit": "mocha src/*-spec.js",
"semantic-release": "semantic-release pre && npm publish && semantic-release post"
},
"devDependencies": {
"ban-sensitive-files": "1.9.0",
"deps-ok": "1.2.0",
"git-issues": "1.3.1",
"license-checker": "11.0.0",
"mocha": "3.4.2",
"nsp": "2.6.3",
"pre-git": "3.15.0",
"prettier-standard": "5.1.0",
"semantic-release": "^6.3.6",
"standard": "10.0.2"
},
"dependencies": {
"ggit": "1.15.1",
"pluralize": "5.0.0"
}
}Yeoman
$ yo node-bahmutov
{
"name": "stop-build",
"version": "0.0.0-development",
"description": "Exits with non-zero code if there are modified Git files",
"author": "Gleb Bahmutov <gleb.bahmutov@gmail.com>",
"bugs": "https://github.com/bahmutov/stop-build/issues",
"config": {
"next-update": {
"commands": {
"pre-git": "./.git/hooks/pre-commit"
}
},
"pre-git": {
"commit-msg": "simple",
"pre-commit": [
"npm run pretest",
"npm run deps",
"npm run ban",
"git add ."
],
"pre-push": [
"npm test",
"npm run secure",
"npm run license",
"npm run ban -- --all",
"npm run size"
],
"post-commit": [],
"post-merge": []
}
},
"engines": {
"node": ">=6"
},
"files": [
"src/*.js",
"!src/*-spec.js"
],
"bin": {
"stop-build": "src/index.js"
},
"homepage": "https://github.com/bahmutov/stop-build#readme",
"keywords": [
"build",
"ci",
"exit",
"git",
"utility"
], "license": "MIT",
"main": "src/",
"publishConfig": {
"registry": "http://registry.npmjs.org/"
},
"repository": {
"type": "git",
"url": "https://github.com/bahmutov/stop-build.git"
},
"scripts": {
"ban": "ban",
"deps": "deps-ok",
"issues": "git-issues",
"license": "license-checker --production --onlyunknown --csv",
"pretty": "prettier-standard 'src/*.js'",
"prelint": "npm run pretty",
"lint": "standard --verbose --fix src/*.js",
"pretest": "npm run lint",
"secure": "nsp check",
"size": "t=\"$(npm pack .)\"; wc -c \"${t}\"; tar tvf \"${t}\"; rm \"${t}\";",
"test": "npm run unit",
"unit": "mocha src/*-spec.js",
"semantic-release": "semantic-release pre && npm publish && semantic-release post"
},
"devDependencies": {
"ban-sensitive-files": "1.9.0",
"deps-ok": "1.2.0",
"git-issues": "1.3.1",
"license-checker": "11.0.0",
"mocha": "3.4.2",
"nsp": "2.6.3",
"pre-git": "3.15.0",
"prettier-standard": "5.1.0",
"semantic-release": "^6.3.6",
"standard": "10.0.2"
},
"dependencies": {
"ggit": "1.15.1",
"pluralize": "5.0.0"
}
}generator-node-bahmutov
Formatting and linting
- Enforce consistent code style using a formatting tool like "prettier"
- Catch simple errors using a linter like "standard"
JavaScript is scripting language ⚠️
Use static linters to catch simple mistakes
Good auto-formatting
Prettier
Prettier is an opinionated code formatter
Static source linter
Standard
One JavaScript Style to Rule Them All
$ npm home prettier
$ npm home standard
{
"scripts": {
"prelint": "prettier-standard '*.js'",
"lint": "standard --fix *.js",
"pretest": "npm run lint",
"test": "exit 1"
}
}package.json
$ npm run lint// index.js
const add = (a, b) => a + b
const sub = (a, b) => {
return a + b
}
module.exports.add = ad
module.exports.sub = sub> standard --fix *.js
my-app/index.js:1:7:
'add' is assigned a value but never used.
my-app/index.js:5:22:
'ad' is not defined.Unit testing JavaScript
Write tests first
Run tests often
Tape, QUnit, Mocha, Ava, Jest
Delightful JavaScript Testing
$ npm install --save-dev jest
$ node_modules/.bin/jest/* eslint-env jest */
describe('add', () => {
const add = require('.').add
it('adds numbers', () => {
expect(add(1, 2)).toBe(3)
})
})$ jest
PASS ./test.js
add
✓ adds numbers (4ms)
Test Suites: 1 passed, 1 total
Tests: 1 passed, 1 total
Snapshots: 0 total
Time: 0.763s, estimated 1s
Ran all test suites. PASS ./test.js
add
✓ adds numbers (7ms)
sub
✓ subs numbers (1ms)
Snapshot Summary
› 2 snapshots written in 1 test suite.it('adds numbers', () => {
expect(add(1, 2)).toMatchSnapshot()
expect(add(100, -50)).toMatchSnapshot()
})$ cat __snapshots__/test.js.snap
// Jest Snapshot v1, https://goo.gl/fbAQLP
exports[`add adds numbers 1`] = `3`;
exports[`add adds numbers 2`] = `50`;Saved snapshot files
expect(value).toMatchSnapshot()
Received value does not match stored snapshot 1.
- 3
+ 21it('adds numbers', () => {
expect(add(1, 20)).toMatchSnapshot()
expect(add(100, -50)).toMatchSnapshot()
})- There are plenty of testing tools and frameworks
- Snapshot testing is becoming mainstream
Unit testing JavaScript
Loading JS Modules
Writing a single JavaScript file is a bad idea, but how should one JS file load another JS file?
CommonJS modules
// add.js
function add (a, b) {
return a + b
}
module.exports = addNode implements CommonJS standard
CommonJS modules
// index.js
const add = require('./add')
add(2, 3) // 5
Node loads a file synchronously
Two huge problems
CommonJS modules
-
Browser cannot load files synchronously
Solution: bundling
add.js sub.js index.js
<script src="bundle.js"></script>bundle.js
Second problem
CommonJS modules
-
JS engine cannot tell what a module exports until it runs module's code
Huge JS bundles because have to include everything, even if code is unused
ES6 Modules
// add.js
export function add (a, b) {
return a + b
}// index.js
import {add} from './add'$ node add.js
./add.js:2
export function add (a, b) {
^^^^^^
SyntaxError: Unexpected token export-
Node 8 does not implement ES6 modules
-
Browser support is patchy
* Target: Node 10, April 2018
*
$ npm i -S @std/esm{
"@std/esm": {
"esm": "js"
},
"scripts": {
"start": "node -r @std/esm index.js"
}
}add to package.json
install dependency
ES6 Modules in Node Today
Building browser bundle
$ npm i -D rollup{
"scripts": {
"build": "rollup index.js -o bundle.js --f iife"
}
}add to package.json
install dependency
$ npm run buildbuild the bundle
Tree-shaking
// index.js
import {add} from './add'
import {sub} from './sub'
console.log(add(2, 3))The bundle is minimal
Thanks, explicit "import / export" declarations!
(function () {
'use strict';
function add (a, b) {
return a + b
}
console.log(add(2, 3));
}());$ cat bundle.jsThere is no "sub" code in the bundle!
<head>
<!-- in case ES6 modules are supported -->
<script src="app/index.js" type="module"></script>
<!-- in case ES6 modules aren't supported -->
<script src="dist/bundle.js" defer nomodule></script>
</head>Browser: ship both bundles
Is this it?
There is so much more
IoT, robots, databases,
WebSockets, Audio and Video, P2P, WebAssembly, VR, compiled to JS languages
JavaScript language is running the modern web
The tools and libraries are incredibly diverse and can satisfy anyone's needs
There is a good process for introducing new language features every year
Modern JavaScript
#boscc
Gleb Bahmutov, PhD
Boston Code Camp 2018
Thank You
Modern JavaScript #boscc Gleb Bahmutov, PhD Boston Code Camp 2018 slides.com/bahmutov/modern-javascript-boscc
Modern JavaScript
By Gleb Bahmutov
Modern JavaScript
Let us look at JavaScript - the language that runs the Internet. We will learn how new features are added to the language, how the modern syntax looks, and the main tools for testing, transpiling and bundling JavaScript applications. Anyone looking to start with JS or upgrade development skills will benefit from this presentation. Presented at Boston Code Camp 2017.
- 5,708
