Typescript Tutorial Development Tutorials, Guides & Insights

function identity<T>(arg: T): T {
  return arg;
}

const result = identity<string>("Hello TypeScript");

You can constrain generics to ensure that the types passed to them meet certain requirements. This is useful when you want to make sure that the generic type has certain properties or methods.

npx tsc

This will output JavaScript files in the dist directory (as specified in tsconfig.json).

npm install --save-dev typescript

Or with yarn:

type Action = 'create' | 'update' | 'delete';
type Entity = 'user' | 'post';

type LogMessage = `${Action}_${Entity}`;

function logAction(action: LogMessage) {
  console.log(`Logging action: ${action}`);
}

logAction('create_user'); // valid
logAction('update_post'); // valid
// logAction('read_user'); // error

function getProperty<T, K extends keyof T>(obj: T, key: K): T[K] {
  return obj[key];
}

const person = { name: 'Alice', age: 30 };

const name = getProperty(person, 'name'); // valid
const age = getProperty(person, 'age');   // valid
// const gender = getProperty(person, 'gender'); // error