Gadget export
From MediaWiki Beginners Wiki
To export the mySandbox gadget, click on "Download" button, save the downloaded file, go to Special:Import on destination wiki and upload it. Then add the following to MediaWiki:Gadgets-definition page:
*mySandbox[ResourceLoader|dependencies=mediawiki.util,mediawiki.Title,mediawiki.Uri|default|rights=createpage]|mySandbox.js
You must have appropriate permissions on destination wiki (including the right to edit system messages) and import from file uploads must be enabled.