A natural use for MLJS is to power the user interface of a browser application. The browser widgets provided in this package, and documented here, allow you to do just this.
These widgets are designed to be used with the JSON results of MLJS calls. Some of them will use MLJS itself to perform searches, for example, but you could pass any JSON in the REST API format to display relevant information.
Be sure to check out the tutorials.
Also read the MLJS Core API documentation.