Manual:Hooks/ResourceLoaderGetConfigVars

Details
ResourceLoaderStartUpModule::getConfig. Use this to export static configuration variables to JavaScript. Things that depend on the current page/request state must be added through MakeGlobalVariablesScript instead.
 * &$vars: Array of variables to be added into the output of the startup module in the form variable name => variable value.

Usage
For instance you want the config variable $mcegConfigVariable to be available in your javascript. Than you functions should look like this: