Change record status: 
Project: 
Introduced in branch: 
8.x
Description: 

All core JavaScript is now using "use strict"; to avoid basic mistakes and issues.

This does not change anything for contrib JavaScript.

MDN: Strict mode.

Updates Done (doc team, etc.)
Online documentation: 
Not done
Theming guide: 
Not done
Module developer documentation: 
Not done
Examples project: 
Not done
Coder Review: 
Not done
Coder Upgrade: 
Not done
Other: 
Other updates done