How to import JavaScript modules in TypeScript

I've got some JavaScript code that I'm trying to convert to Typescript.

Supposedly, typescript is a superset of JavaScript, except the following has compiler errors. Assuming I didn't import the ko library into typescript, how would I convert the following code:

(function(ko, viewModels){
    viewModels.MyViewModel = function(){
        //stuff in here
    }
}(ko, window.viewModels = window.viewModels || {}));

For references, this was my attempt in TypeScript

module viewModels {

    export class PartDetailsViewModel {
        public bar: string;
             constructor (){
                 this.bar = ko.foo(); //<-- compiler error, "ko" does not exist in current scope
             }
        }
    }
}