Manual:$wgLegacyJavaScriptGlobals

ResourceLoader: $wgLegacyJavaScriptGlobals
Whether or not to assign configuration variables to the global window object.
Introduced in version:1.18.0 (r87856)
Deprecated in version:1.35.0 (Gerrit change 618030; git #0b23e103)
Removed in version:1.37.0 (Gerrit change 678716; git #99d4ad59)
Allowed values:(boolean)
Default value:false (1.35-1.36)
true (1.18-1.34)

Details edit

Whether or not to assign configuration variables to the global window object.

If this is set to false, old code using deprecated variables like:

if ( window.wgRestrictionEdit ) ...

or:

if ( wgIsArticle ) ...

will no longer work and needs to use mw.config instead. For example:

if ( mw.config.exists('wgRestrictionEdit') )

or:

if ( mw.config.get('wgIsArticle') )