User:Enterprisey/sync-template-sandbox.js

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$( function() {
    // 10 is "Template:" and 828 is "Module:"
    if ( ( mw.config.get( "wgNamespaceNumber" ) === 10 || mw.config.get( "wgNamespaceNumber" ) === 828 ) && mw.config.get( "wgPageName" ).includes( "/sandbox" ) ) {
        var link = mw.util.addPortletLink(
            "p-cactions",
            "#",
            "Sync with main",
            "ca-sync",
            "Overwrite the sandbox code with the code from the main template"
        );
        mw.loader.using( "mediawiki.api", function () {
            link.addEventListener( "click", function () {
                var api = new mw.Api();
                api.get( {
                    prop: 'revisions',
                    rvprop: 'content',
                    rvlimit: 1,
                    titles: mw.config.get( "wgPageName" ).replace( "/sandbox", "" )
                } ).done( function ( data ) {
                    if ( !data.query || !data.query.pages ) return;
                    var pageid = Object.getOwnPropertyNames( data.query.pages )[0],
                        text = data.query.pages[pageid].revisions[0]["*"];
                    api.postWithEditToken( {
                        action: "edit",
                        title: mw.config.get( "wgPageName" ),
                        summary: "Syncing sandbox code with main template ([[User:APerson/sync-template-sandbox|sync-template-sandbox.js]])",
                        text: text
                    } ).done ( function ( data ) {
                        if ( data && data.edit && data.edit.result && data.edit.result == 'Success' ) {
                            mw.notify( "Synced successfully! Reloading in 5 seconds..." );
                            window.setTimeout( function () {
                                document.location.reload( true );
                            }, 5000 );
                        }
                    } );
                } );
            } );
        } );
    }
} );