Code reference information
WebStorm shows you reference for standard APIs, for symbols from your project and from its dependencies, as well as for symbols defined in external libraries. You can view the documentation for symbols in the Documentation popup and open documentation on external sites if links to them are available.
For most HTML tags and for some attributes WebStorm can show you a summary from the corresponding MDN article.
In addition to reference information in the Documentation popup and tool window, WebStorm shows Inlay Hints right in the editor. These can be names and types of parameters, variables, and fields, return types of called functions and methods, special values, inheritors and usages, and other hints.