Learn TypeScript 3 by Building Web Applications

An example with classes

You can, of course, also use generics in your class definitions:

class NaiveMap<Key, Value> { private _keys: Key[] = []; private _values: Value[] = []; constructor(){} contains(key: Key): boolean { const result = this._keys.indexOf(key); return result !== -1; } put(key: Key, value: Value): void { if(!this.contains(key)) { this._keys.push(key); this._values.push(value); } } get(key: Key): Value | undefined { if(this.contains(key)) { return this._values[this._keys.indexOf(key)]; } else{ return undefined; } } } class Thing { constructor(public name: string){} } const naiveMap = new NaiveMap<string, Thing>(); naiveMap.put("foo", new Thing("The thing")); console.log(naiveMap.contains("foo")); // true console.log(naiveMap.get("foo")); ...