Four steps from JavaScript to TypeScript

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4 STEPS FROM JAVASCRIPT TO TYPESCRIPT @philnash

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Phil Nash @philnash https://philna.sh [email protected]

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4 STEPS FROM JAVASCRIPT TO TYPESCRIPT @philnash

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I 💖 JAVASCRIPT @philnash

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WHAT ABOUT TYPESCRIPT? @philnash

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Modern JavaScript development • Bigger projects • Bigger teams • More tools @philnash

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Reasons to move to TypeScript • Type safety • Tooling • Refactoring • Confidence @philnash

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Reasons not to move to TypeScript • Learning curve • Overhead • "You don't need tests" • New JS features @philnash

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IT'S UP TO YOU AND YOUR TEAM @philnash

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MOVE TO TYPESCRIPT @philnash

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INTRODUCING THE DEMO APPLICATION @philnash

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STEP 1: PAIR PROGRAM WITH TYPESCRIPT @philnash

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I 💖 VSCODE @philnash

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TYPESCRIPT IS BUILT IN @philnash

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DEMO @philnash

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Downsides • It's only in the editor • Native in VSCode and Atom • TypeScript comments in a JS codebase @philnash

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RECOMMENDATION: TURN IT ON GLOBALLY IN YOUR EDITOR @philnash

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STEP 2: GET STARTED WITH THE TYPESCRIPT COMPILER @philnash

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Time to install TypeScript npm install typescript --save-dev @philnash

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Initialise the project npx tsc --init @philnash

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tsconfig.json { "compilerOptions": { "target": "es5", "module": "commonjs", "esModuleInterop": true, "skipLibCheck": true, "forceConsistentCasingInFileNames": true } } 01. 02. 03. 04. 05. 06. 07. 08. 09. @philnash

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tsconfig.json { "compilerOptions": { "target": "esnext", "module": "commonjs", "allowJS": true, "checkJS": false, "outDir": "./dist", "rootDir": "./src", "strict": false, ... } } 01. 02. 03. 04. 05. 06. 07. 08. 09. 10. 11. 12. @philnash

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Update package.json { "main": "dist/index.js", "scripts": { "build": "tsc", "watch": "tsc --watch" } } 01. 02. 03. 04. 05. 06. 07. @philnash

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DEMO @philnash

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STEP 3: CHECK JAVASCRIPT WITH TYPESCRIPT @philnash

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tsconfig.json { "compilerOptions": { "target": "esnext", "module": "commonjs", "allowJS": true, "checkJS": true, ... } } 01. 02. 03. 04. 05. 06. 07. 08. 09. @philnash

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Types for Node.js npm install @types/node --save-dev @philnash

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DEFINITELY TYPED @philnash

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DEMO @philnash

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STOP THERE? @philnash

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Compiling JavaScript with TypeScript • TypeScript is type checking the JavaScript • You can add further type annotations with JSDoc • You don't need to output anything @philnash

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BE LIKE WEBPACK @philnash

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tsconfig.json { "compilerOptions": { // "outDir": "./dist", "noEmit": true, ... } } 01. 02. 03. 04. 05. 06. 07. @philnash

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JSDOC: TYPESCRIPT WITHOUT WRITING TYPESCRIPT @philnash

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JSDoc /** * @type string */ let foo; 01. 02. 03. 04. @philnash

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JSDoc /** * @param {number} a * @param {number} b * @returns {number} */ function add(a, b) { return a + b; } 01. 02. 03. 04. 05. 06. @philnash

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DEMO @philnash

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STEP 4: MOVING TO TYPESCRIPT @philnash

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🎉 FINALLY 🎉 @philnash

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.js => .ts @philnash

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DEMO @philnash

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STRICT @philnash

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Strict tsconfig options • noImplicitAny • noImplicitThis • strictBindCallApply • strictNullChecks • strictFunctionTypes • strictPropertyInitialization • alwaysStrict @philnash

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Strict tsconfig options • strict @philnash

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DEMO @philnash

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FULL STRICT MODE IS NOT REQUIRED @philnash

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BUT IT CAN BE A GOAL @philnash

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MORE TYPES @philnash

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DEMO @philnash

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LIBRARY DEVELOPMENT @philnash

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Library development { "compilerOptions": { "declaration": true, ... } } 01. 02. 03. 04. 05. 06. @philnash

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WE MADE IT! @philnash

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STEP 1: PAIR PROGRAM WITH TYPESCRIPT @philnash

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STEP 2: GET STARTED WITH THE TYPESCRIPT COMPILER @philnash

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STEP 3: CHECK JAVASCRIPT WITH TYPESCRIPT @philnash

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STEP 4: MOVE TO TYPESCRIPT @philnash

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Resources The demo repo https://github.com/philnash/four-steps-from-javascript-to-typescript @philnash

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Resources Move your project to TypeScript at your own pace Dominik Kundel — https://www.twilio.com/blog/move-to-typescript TypeScript without TypeScript — JSDoc Superpowers Stefan Baumgartner — https://fettblog.eu/typescript-jsdoc-superpowers/ JS Projects Utilizing TypeScript TypeScript docs — https://www.typescriptlang.org/docs/handbook/intro-to-js-ts.html @philnash

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Other links Definitely Typed: The Movie John Reilly — https://blog.johnnyreilly.com/2019/10/definitely-typed-movie.html The TypeScript Tax Eric Elliott — https://medium.com/javascript-scene/the-typescript-tax-132ff4cb175b @philnash

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Thanks! @philnash https://philna.sh [email protected]