Since WebStorm 2020.2, JSLint support in the IDE has been deprecated.
However, JSLint support is still available through the JSLint plugin, which can be installed on the Settings/Preferences | Plugins page as described in Installing plugins from JetBrains repository.
Note that JSLint does not fully support some latest ECMAScript features, see the JSLint official website for details.
When JSLint support is enabled, WebStorm highlights errors that JSLint detects, provides descriptions for them, and suggests quick-fixes where possible.
Descriptions of the errors detected in the current file and quick-fixes for them are available from the editor and from the Current File tab of the Problems tool window.
Errors in all previously opened files and quick-fixes for them are shown in the Project Errors tab of the Problems tool window. To open the tool window, click the Inspection widget in the upper-right corner of the editor:
Enable JSLint and configure its behavior in WebStorm
In the Settings/Preferences dialog Ctrl+Alt+S, go to Languages and Frameworks | JavaScript | Code Quality Tools | JSLint, and select the Enable checkbox. After that the other controls on the page become available.
By default, the tool reports detected problems of all types. To skip problems of a certain type, select the checkbox next to this type in the Tolerate area.