Xrm.WebApi.retrieveMultipleRecords
is available on CRM form.
Is there any way to query web api from the javascript on webpages?
Unfortunately we cannot use Xrm.WebApi
in portals and they are native to CRM forms.
Recently web api is introduced for portals and you can use it for CUD operations from portal. MS documentation and this blog post can help you to understand and setup the pre-requisites like enabling settings, permissions, verbose.
For entity data retrieval - still we have to use fetchxml
liquid tag. Read more