> services.Http.get("api/matrixTemplates/getAttributeValues/" + id + "/" + criteria);
>
>My question to you is - how exactly I need to code the above so it would work for any character criteria?

You shouldn't have to encode anything because the XHR request (ie. the Webrequest internal tot the browser) will automatically fix up the URL. If you want to be extra safe and don't rely on that behavior you can UrlEncode the parameterized value.

Either way passing a parameters object in the .get() call will never fill these parameters - you need to hard code those as you show above or by using `encodeURIComponent()` to encode the values.

services.Http.get("api/matrixTemplates/getAttributeValues/" + encodeURIComponent(id) + "/" + encodeURIComponent(criteria));

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/encodeURIComponent