Implement an indexible interface

Question

How would I implement an interface that is indexible:

interface fooInterface{
    // indexable
    [index:string]:number;
    [index:number]:number;                 


        

Answer 1

You don't ever implement it in the class definition, but only by addressing instance[index], so your fooInterface cannot be be used via implements on a TypeScript class, but can be used to describe the expected structure of an object, e,g. var foo: fooInterface = {};

Describing an Indexable Object

A common pattern in JavaScript is to use an object (e.g. {}) as way to map from a set of strings to a set of values. When those values are of the same type, you can use an interface to describe that indexing into an object always produces values of a certain type (in this case, Widget).

interface WidgetMap {
    [name: string]: Widget;
}

var map: WidgetMap = {};
map['gear'] = new GearWidget();
var w = map['gear']; // w is inferred to type Widget

Quote and Widget example taken from: http://blogs.msdn.com/b/typescript/archive/2013/01/24/interfaces-walkthrough.aspx