[javascript] ES6 Map in Typescript

I'm creating a class in typescript that has a property that is an ES6 (ECMAscript 2016) Map like so:

class Item {
  configs: ????;
  constructor () {
    this.configs = new Map();
  }
}

How do I declare an ES6 Map type in typescript?

This question is related to javascript typescript typescript1.5

The answer is


Not sure if this is official but this worked for me in typescript 2.7.1:

class Item {
   configs: Map<string, string>;
   constructor () {
     this.configs = new Map();
   }
}

In simple Map<keyType, valueType>


Here is an example:

this.configs = new Map<string, string>();
this.configs.set("key", "value");

Demo


See comment in: https://github.com/Microsoft/TypeScript/issues/3069#issuecomment-99964139

TypeScript does not come with built in pollyfills. it is up to you to decide which pollyfill to use, if any. you can use something like es6Collection, es6-shims, corejs..etc. All the Typescript compiler needs is a declaration for the ES6 constructs you want to use. you can find them all in this lib file.

here is the relevant portion:

interface Map<K, V> {
    clear(): void;
    delete(key: K): boolean;
    entries(): IterableIterator<[K, V]>;
    forEach(callbackfn: (value: V, index: K, map: Map<K, V>) => void, thisArg?: any): void;
    get(key: K): V;
    has(key: K): boolean;
    keys(): IterableIterator<K>;
    set(key: K, value?: V): Map<K, V>;
    size: number;
    values(): IterableIterator<V>;
    [Symbol.iterator]():IterableIterator<[K,V]>;
    [Symbol.toStringTag]: string;
}

interface MapConstructor {
    new <K, V>(): Map<K, V>;
    new <K, V>(iterable: Iterable<[K, V]>): Map<K, V>;
    prototype: Map<any, any>;
}
declare var Map: MapConstructor;

Typescript does not yet support Map.

ES6 Compatibility Table


How do I declare an ES6 Map type in typescript?

You need to target --module es6. This is misfortunate and you can raise your concern here : https://github.com/Microsoft/TypeScript/issues/2953#issuecomment-98514111


As a bare minimum:

tsconfig:

 "lib": [
      "es2015"
    ]

and install a polyfill such as https://github.com/zloirock/core-js if you want IE < 11 support: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map


With the lib config option your are able to cherry pick Map into your project. Just add es2015.collection to your lib section. When you have no lib config add one with the defaults and add es2015.collection.

So when you have target: es5, change tsconfig.json to:

"target": "es5",
"lib": [ "dom", "es5", "scripthost", "es2015.collection" ],

Yes Map is now available in typescript.. if you look in lib.es6.d.ts, you will see the interface:

interface Map<K, V> {
  clear(): void;
  delete(key: K): boolean;
  forEach(callbackfn: (value: V, key: K, map: Map<K, V>) => void,thisArg?: any): void;
  get(key: K): V | undefined;
  has(key: K): boolean;
  set(key: K, value: V): this;
  readonly size: number;} 

Its great to use as a dictionary of string,object pairs.. the only annoyance is that if you are using it to assign values elsewhere with Map.get(key) the IDE like Code gives you problems about being possible undefined.. rather than creating a variable with an is-defined check .. simply cast the type (assuming you know for sure the map has the key-value pair)

class myclass {
   mymap:Map<string,object>
   ...
   mymap = new Map<string,object>()
   mymap.set("akey",AnObject)
   let objectref = <AnObject>mymap.get("akey")

Add "target": "ESNEXT" property to the tsconfig.json file.

{
    "compilerOptions": {
        "target": "ESNEXT" /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', or 'ESNEXT'. */
    }
}