ES6 Map in Typescript

Question

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

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As a bare minimum   tsconfig     lib            es2015          and install a polyfill such as https   github com zloirock core-js if you want IE  lt  11 support  https   developer mozilla org en-US docs Web JavaScript Reference Global Objects Map

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Here is an example   this configs   new Map lt string  string gt     this configs set  key    value      Demo

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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

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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 lt K  V gt        clear    void      delete key  K   boolean      entries    IterableIterator lt  K  V  gt       forEach callbackfn   value  V  index  K  map  Map lt K  V gt     gt  void  thisArg   any   void      get key  K   V      has key  K   boolean      keys    IterableIterator lt K gt       set key  K  value   V   Map lt K  V gt       size  number      values    IterableIterator lt V gt        Symbol iterator    IterableIterator lt  K V  gt        Symbol toStringTag   string     interface MapConstructor       new  lt K  V gt     Map lt K  V gt       new  lt K  V gt  iterable  Iterable lt  K  V  gt    Map lt K  V gt       prototype  Map lt any  any gt     declare var Map  MapConstructor

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EDIT  Jun 5 2019   While the idea that  quot TypeScript supports Map natively quot  is still true  since version 2 1 TypeScript supports something called Record  type MyMapLikeType   Record lt string  IPerson gt   const peopleA  MyMapLikeType          quot a quot     name   quot joe quot          quot b quot     name   quot bart quot         Unfortunately the first generic parameter  key type  is still not fully respected  even with a string type  something like peopleA 0   a number  is still valid   EDIT  Apr 25 2016   The answer below is old and should not be considered the best answer  TypeScript does support Maps  quot natively quot  now  so it simply allows ES6 Maps to be used when the output is ES6  For ES5  it does not provide polyfills  you need to embed them yourself  For more information  refer to mohamed hegazy s answer below for a more modern answer  or even this reddit comment for a short version   As of 1 5 0 beta  TypeScript does not yet support Maps  It is not yet part of the roadmap  either  The current best solution is an object with typed key and value  sometimes called a hashmap   For an object with keys of type string  and values of type number  var arr      key string  number           Some caveats  however   keys can only be of type string or number It actually doesn t matter what you use as the key type  since numbers strings are still accepted interchangeably  only the value is enforced    With the above example     OK  arr  quot name quot     1     String key is fine arr 0    0     Number key is fine too     Not OK  arr   a   quot a quot       2     Invalid key arr 3     quot name quot      Invalid value

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Add  target    ESNEXT  property to the tsconfig json file          compilerOptions              target    ESNEXT     Specify ECMAScript target version   ES3   default    ES5    ES2015    ES2016    ES2017   or  ESNEXT

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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

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Yes Map is now available in typescript    if you look in lib es6 d ts  you will see the interface   interface Map lt K  V gt      clear    void    delete key  K   boolean    forEach callbackfn   value  V  key  K  map  Map lt K  V gt     gt  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 lt string object gt            mymap   new Map lt string object gt       mymap set  akey  AnObject     let objectref    lt AnObject gt mymap get  akey

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Typescript does not yet support Map   ES6 Compatibility Table

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Not sure if this is official but this worked for me in typescript 2 7 1   class Item      configs  Map lt string  string gt      constructor           this configs   new Map             In simple Map lt keyType  valueType gt

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