Can I define a Typescript class which has an index signature?

Question

I have an interface type called IRawParams which simply specifies a string key and any vals.

interface IRawParams {     [key: string]: any } 

I have a class, ParamValues which contains some behavior on top of keys/values. I'd like to specify that the ParamValues class implements IRawParams interface.

class ParamValues implements IRawParams {     parseFromUrl(urlString: string) {         Parser.parse(urlString).forEach(item => this[item.key] = item.val);     } }  // so I can do something like this var params = new ParamValues(); params.parseFromUrl(url); var userId = params.userId; 

When I attempt this, I get a compiler error:

error TS2420: Class 'ParamValues' incorrectly implements interface 'IRawParams'. Index signature is missing in type 'ParamValues'.

Can I get my class to implement the IRawParams Interface, or otherwise get Typescript to allow instances of my class to be compatible with an indexed type {[key: string]: any}?

Answer 1

To define a class with an index signature, just write the index signature in the class:

interface IRawParams {     [key: string]: any }  class Foo implements IRawParams {     [k: string]: any; }