Implementing an indexer in a class in TypeScript

class typescript indexer
MgSam picture MgSam · Feb 12, 2013 · Viewed 24.5k times · Source

Is it currently possible to implement an indexer on a class in TypeScript?

class MyCollection {
   [name: string]: MyType;       
}

This doesn't compile. I can specify an indexer on an interface, of course, but I need methods on this type as well as the indexer, so an interface won't suffice.

Thanks.

Answer

Fenton picture Fenton · Feb 13, 2013

You cannot implement a class with an indexer. You can create an interface, but that interface cannot be implemented by a class. It can be implemented in plain JavaScript, and you can specify functions as well as the indexer on the interface:

class MyType {
    constructor(public someVal: string) {

    }
}

interface MyCollection {   
   [name: string]: MyType;
}

var collection: MyCollection = {};

collection['First'] = new MyType('Val');
collection['Second'] = new MyType('Another');

var a = collection['First'];

alert(a.someVal);

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