Typescript Dictionary

my-dict.ts

type KEY = string | number | symbol;

interface Dictionary<K extends KEY, V> {
  getKeys(): K[];
  getValues(): V[];
  get(key: K): V | null;
  put(key: K, val: V): void; // or boolean?
}

class JSDict<K extends KEY, V> implements Dictionary<K, V> {

	private dict: { [key in K]?: V };

	constructor() {
		this.dict = {};
	}

	public getKeys() {
		let keys: K[] = [];
		for(let key in this.dict) {
			keys.push(key);
		}

		return keys;
	}

	public getValues() {
		let vals: V[] = [];
		for (let key in this.dict) {
			let v = this.dict[key];

			if (this.exists(v)) {
				vals.push(v);
			}
		}

		return vals;
	}

	// Type predicate to ensure v exists
	private exists(v: V | undefined): v is V {
		return v != null && typeof v !== "undefined";
	}

	public get(key: K) {
		let v = this.dict[key];

		return this.exists(v)
			? v
			: null;
	}

	public put(key: K, val: V) {
		this.dict[key] = val;
	}

	static Create<Keys extends KEY, Values>() {
		return new JSDict<Keys, Values>();
	}
}


type Fruits = "Apples" | "Bananas" | "Oranges"; 

var d = JSDict.Create<Fruits, number>();
d.put("Bananas", 5);

// etc...

Maybe I should just use mapped types directly - rewrite incoming