The ArcGIS API for JavaScript™ (JavaScript API) is a browser based API for developing high performance, easy to use mapping applications. The API allows you to easily embed maps in your Web pages. The JavaScript API is hosted by ESRI on ArcGIS Onlin

The catalog resource is the root node and initial entry point into an ArcGIS Server host. This resource represents a catalog of folders and services published on the host.

The current version of the server is also returned in the response (introduced at 9.3.1). The value of the version is a number such that its value at a future release is guaranteed to be greater than its value at a previous release.

The ArcGIS JavaScript API is a lightweight way to embed your GIS maps and tasks in Web applications. It's easy to build and deploy applications built with this API. All you need is an ArcGIS Server available whose maps and tools you can use in your application.