All JavaScript is valid TypeScript

Here's some TypeScript code:

const array = [1, 2, 3, 4, 5]

function squareNumber(num) {
    return num * num
}

const squared = array.map(squareNumber)

squared // [1, 4, 9, 16, 25]
array // [1, 2, 3, 4, 5]

const doubled = array.map(num => num * 2); // [2, 4, 6, 8, 10]

const books = [
    {
        name: "JavaScript: The Definitive Guide",
        description: `Since 1996, JavaScript: The Definitive Guide...`,
        price: 28.89
    },
    {
        name: "Eloquent JavaScript",
        description: `JavaScript lies at the heart...`,
        price: 21.22
    },
    {
        name: "JavaScript: The Good Parts",
        description: `Most programming languages...`,
        price: 16.59
    }
];

const getTitle = book => book.name;

const titles = books.map(getTitle);

const titlesOfExpensiveBooks = books
    .filter(book => book.pirce > 20)
    .map(getTitle);

What's the point then? Let's take a look.

Benefits of TypeScript

• type safety (duh...)
• your editor get's smarter
• no need for as many unit tests
• almost no entry cost if you know JS already
• most (?) of the latest JS features

By the way

During this workshop we'll be using the latest version (3.6.2) that was installed by create-react-app when creating a new project.

If you didn't create a project yet, now's the last chance, here's what to do:

npm i -g create-react-app
create-react-app react-ts-devmeeting --typescript
cd react-ts-devmeeting
npm start

Resources

• Typescript playground