Manual:Hooks/MakeGlobalVariablesScript

Details
Called right before Skin::makeVariablesScript is executed. Ideally, this hook should only be used to add variables that depend on the current page/request; static configuration should be added through ResourceLoaderGetConfigVars instead.
 * &$vars: variable (or multiple variables) to be added into the output of Skin::makeVariablesScript
 * $out : OutputPage instance calling the hook
 * &$wgUser : user (object) who is loading the skin. This was added in r43592 and removed in r43632.