Meetup Paris Typescript – 2016/11/24 - @Dashlane Power Leveling your Typescript From beginner to master in no time ! 

Who am I ? Experienced developer focusing on web for 5 years @2016 getting things done at Dashlane https://github.com/Offirmo 

Welcome to the world of TypeScript www.typescriptlang.org 

So you want to become a typescript master ? Prove your worth. 

“I want code that compile” « As an enterprise web application developer, I don't like any scripting or dynamic languages. I like code that compiles (...) TypeScript looks like it will help with some of the problems like having (...) compiling (…) » (somewhere on the net) No. You are asking for a linter. All languages have linters. JS already has an excellent linter: ESLlint TypeScript also has a linter: TSLint They will catch typos and code smells. Use a linter. Now. 

“Company BIG™ is using it” ● Created by Microsoft ● Embraced by Google: Angular 2 ● Big contributions from Palantir (tslint, blueprint, …) ● Webpack is considering a rewrite in typescript Following strong players’ lead may be a good move, But could you make your own opinion ? 

Yes or No ? ● Editor auto-completion ● Types = documentation – Collaboration – Faster usage ● Types = catching (some) errors – Interfaces – early ● Refactoring ● ... ● New language to learn ● NOT trivial ● More complicated stack ● Typings (find, fix, update…) ● Source maps ● Can’t use some JS tooling ● Bugs ● Lagging behind the standard ● Static typing sometimes refuses good programs and has to be painfully hacked ● ... 

Yes or No ? ● Editor auto-completion ● Types = documentation – Collaboration – Faster usage ● Types = catching (some) errors – Interfaces – early ● Refactoring ● ... ● New language to learn ● NOT trivial ● More complicated stack ● Typings (find, fix, update…) ● Source maps ● Can’t use some JS tooling ● Bugs ● Lagging behind the standard ● Static typing sometimes refuses good programs and has to be painfully hacked ● ... Short-term Long-term & important 

Quick check ● Do you work in a team ? (3+) ● Do you have time right now ? ● Is it a long-term project or just a MVP ? ● Are you experienced ? ● Does your industry need the best ? (ex. Security) ● Do you like Typescript ? 

Don’t ! ● Not a substitute for Unit Tests ● Not a substitute for Code Reviews ● Not a way to go back to your OOP comfort zone – Please learn about functional programming  A Gentle Introduction to Functional JavaScript 

Quest cleared ! “Understand why using typescript” 

New Quest: “Hello World in Typescript” Do the tutorial: https://www.typescriptlang.org/docs/tutorial.html 

Which Typescript ? Go straight at TypeScript 2 (which is latest at this time 2016/11/24) npm i –save-dev typescript yarn add –dev typescript 

Setup typescript: “tsconfig.json” https://www.typescriptlang.org/docs/handbook/tsconfig-json.html https://www.typescriptlang.org/docs/handbook/compiler-options.html files to compile must be declared (more about this later) { "compileOnSave": false, "compilerOptions": { "allowJs": false, "noEmitOnError": true, "noImplicitAny": true, (...) "strictNullChecks": true, "target": "ES6", "module": "ES6", "declaration": true, "sourceMap": true, "outDir": “temp/src.es6" }, "include": [ "src/**/*.ts" ], "exclude": [ "node_modules" ] } new project from scratch or from existing code ? choose the errors to catch ! or else your IDE may launch transpilation ! output control 

Quest cleared ! “Hello typescript” 

Side-quest: “Know your transpiler” Module ES6 CommonJS AMD UMD SystemJS Target ES3 ES5 ES6 You can pick whatever combo (Module + Target) 

Execute typescript: node 6 example Target: node v6 99% ES6 CommonJS tsc target = ES6 module = commonjs Source: Typescript 100% ES6, ?% ES7 ES6 modules 

Execute typescript: node 4 example tsc target = ES6 module = ES6 Target: node v4 57% ES6 CommonJS tsc target = ES5 module = commonjs Source: Typescript 100% ES6, ?% ES7 ES6 modules Intermediate: ES6 100% ES6 ES6 modules babel babel-preset-es2015- node4 FYI: an alternative stack ☟ 

New Quest: “Get Things Done in Typescript” 

Write types ! ● boolean ● number ● string ● void ● Function ● null ● undefined Combine them: Interface Person { name: string age: number friends: Person[] } https://www.typescriptlang.org/docs/handbook/basic-types.html 

Nullable by default ! interface Foo { name: string age: number } interface Foo { name: string age: number | undefined } const x: Foo = { name: undefined, age: undefined } const x: Foo = { name: undefined, age: undefined } "StrictNullChecks": true (tsconfig.json) 

enum vs. unions const enum Directions { Up, Down, Left, Right } type Directions = 'up' | 'down' | 'left' | 'right' https://www.typescriptlang.org/docs/handbook/enums.html ↓This writing is very convenient 

Type vs. Interface ● Use interface for grouping ● Use type to define aliases: type TimeoutMs = number type AdventureModel = JsonSchemaBasedModel 

Modules Detection ● If no exports, not a module = global variables 

Argument destructuring function displayPopup( {onCancel, onConfirm}: {onCancel:()=>void, onConfirm:()=>void} ): void { … interface Params { onCancel: () => void onConfirm: () => void } function displayPopup({onCancel, onConfirm}: Params): void { ... https://www.barbarianmeetscoding.com/blog/2016/05/13/argument-destructuring-and-type-annotations-in-typescript/ 

Hashes and JSON ● Hashes can be typed: interface Colors {[k: string]: Color } ● JSON is a declared type, can be extended: interface JsonSchema extends JSON { title: string additionalProperties: boolean [k: string]: any } 

overloading ● Not that simple. Better handled in code itself. function hello(locutor: string, ...locutors: string[]): void { locutors.unshift(locutor) console.log(`Hello, ${locutors.join(', ')} !`) } hello('typescript world') hello('Joe', 'Jack', 'William', 'Averell') 

Type limitations ● Object.assign() => use as … ● .bind() => use ES6 

Casting: as X, as any as X ● Casting from compatible type: let x: any = { name: ‘Lothar’, age: 32 } let user: Person = x as Person ● Force casting let x: any = { name: ‘Lothar’ } let user: Person = x as any as Person Don’t overuse it ! Valid use case: mock data in tests 

typeof import * as axios from 'axios' interface Dependencies { axios: typeof axios } ● smell ● hack 

Can you feel your growth ? 

Use a npm module import { debounce } from lodash Error ! Typescript CAN NOT consume Javascript (directly) 

Boss: “Dark Typings” This boss can never be defeated, only repelled :-( 

Need to use a “declaration file” (aka “typing”) ● A special kind of TypeScript file which “annotate” some JS: npm I -D @types/lodash ● You NEED them. But may not exist, not be correct, not be up-to-date ● @types picked automatically by the compiler (since typescript 2) ● Sometimes needed: import * as _ from ‘lodash’ ● Write your own: official doc, tutorial (More about this in next talk !) http://stackoverflow.com/questions/38224232/how-to-consume-npm-modules-from-typescript 

Boss chased away ! 

Choose your class to progress further… Back-end (node) Front-end (browser) Universal (modules) 

Back-end ● The simplest ;) ● npm I -D @types/node ● Execute directly: ts-node – With a shebang 

Front-end Webpack ● typescript loader: ts-loader React ● Complete class example here ● Special linting rules: tslint-react ● Typed CSS: typestyle ● limitations Angular 2 ● (see tutorials) 

Execute typescript: browser Target: browser ES5 bundled webpack + ts-loader + babel (for ES6 modules) Source: Typescript 100% ES6, ?% ES7 ES6 modules See also awesome-typescript-loader 

Execute typescript: browser tsc target = ES6 module = ES6 +npm/cpx Target: browser ES5 bundled Source: Typescript 100% ES6, ?% ES7 ES6 modules Intermediate: ES6 100% ES6 ES6 modules + css, png... webpack +babel FYI an alternate 2-steps stack which allows to use create-react-app without modification 

(npm) npm-run + cpx package.json/scripts "dev1": "tsc --watch", "dev2": "cpx 'src-ts/**/*.{json,css,png}' src", "dev": "run-p dev1 dev2", 

Universal (module) ● Generate several versions of your code: node stable, ES6, UMD ● Generate and expose the typings ● NEVER use default exports: babel and typescript won’t work well (see next slide) ● Beware of conflicting environments – Node vs. browser on SetTimeout 

ES6 exports: no default ! ● export default doesn’t play well with all platforms ● Use only named exports export { Foo, bar } ● Named exports are recommended in TypeScript regardless of this issue ● Interesting reads: – http://stackoverflow.com/a/38671949/587407 – http://blog.jonasbandi.net/2016/10/myth-of-superset.html#comment-29295611 55 – http://www.jbrantly.com/es6-modules-with-typescript-and-webpack/ – https://github.com/webpack/webpack/issues/706 

Real example of a universal TS npm module ● https://github.com/Offirmo/hello-world-npm ● All envs testable with – https://github.com/Offirmo/cross-js-env-tests 

Quest achieved 

Next quests: “Advanced” ● Example of ts tyleguide: typescript coding guidelines ● TypeScript formatter: tsfmt ● Call the typescript compiler from a script: – node-typescript-compiler – Allows to dynamically change config ● Useful npm script: syntax watch: "tsc:watch": "npm run tsc -- --watch", ● In special cases, you may have to tweak the –lib option: --lib webworker 

Final words: Superset ? ● Superset of JavaScript ? ● Comparison : C++ superset of C ? ● Superset of WELL-WRITTEN JavaScript ? ● http://blog.jonasbandi.net/2016/10/myth-of-superset.html#co mment-2929561155 https://smellegantcode.wordpress.com/2015/07/11/is-typescript-really-a-superset-of-javascript-and-does-it-even-matter/ 

Thank you 

Sources ● http://stackoverflow.com/questions/tagged/typescript?sort=frequent&pageSize=50 ● https://www.reddit.com/r/typescript/comments/3fp1l2/why_bother_with_typescript/ ● http://www.aaron-powell.com/posts/2013-01-07-thoughts-on-typescript.html ● https://smellegantcode.wordpress.com/2015/07/11/is-typescript-really-a-superset-of-javascript-and-does-it-even-matter/ ● https://github.com/Offirmo-team/wiki/wiki/typescript ● I was wrong about typescript https://news.ycombinator.com/item?id=11841502 ● http://www.jbrantly.com/es6-modules-with-typescript-and-webpack/ ● http://www.jbrantly.com/typescript-and-webpack/ ● 

Resources ● http://mogmygear.com/index.php ● http://reznik.wikia.com/wiki/Axxa's_Wow_Logo_Creator ● http://achievementgen.com/wow/ ● http://eu.battle.net/wow/fr/media/wallpapers/