The bad reasons

With TypeScript, no need for writing tests

With TypeScript, I can trust my code at runtime

1interface Person {
2    id: string;
3    name: string;
4}
5
6function sayHello(person: Person) {
7    console.log(person.name);
8}
9
10sayHello({} as any);

TypeScript looks more like C#, I don’t need to understand JavaScript

The good reasons

TypeScript will help your developers work together on a growing codebase

TypeScript tools will save your developers time

• tsserver

• Language Servers Protocol Project

• Others tools and initiatives

The Microsoft community-effort success story

• React “integrated” propsTypes
  “Native” mapping between TypeScript types and React PropTypes.

1// without TypeScript
2
3import PropTypes from 'prop-types';
4
5class Greeting extends React.Component {
6  render() {
7    return (
8      <h1>Hello, {this.props.name}</h1>
9    );
10  }
11}
12
13Greeting.propTypes = {
14  name: PropTypes.string
15};
16
17// With TypeScript (no 'prop-types' import needed, and no config)
18type Props = { name: string };
19class Greeting extends React.Component<Props> {
20  render() {
21    return (
22      <h1>Hello, {this.props.name}</h1>
23    );
24  }
25}

• DefinitelyTyped @types

• ApolloData GraphQL types generation

TypeScript gives you a taste of future JavaScript, with typings

Summary

Bad

• Test replacement, TypeScript ain’t a test framework
• Runtime safety, TypeScript ain’t a runtime type checker
• I can write object-oriented C# a-like code, TypeScript is typed JavaScript

Good

• Team and code scalability with “Interface oriented development”
  TypeScript will help you deal with growing teams and large codebase
• Tooling and Community
  Microsoft made an awesome community effort work.
• ES-next compliance
  TypeScript give you a taste of future JavaScript, with typing.