#target Indesign
var doc = app.activeDocument;
var mySel = app.selection[0];
if (mySel) {
    var sb = mySel.geometricBounds;
    //https://forums.adobe.com/message/3869567#3869567
    var bkp = app.marginPreferences.properties;
    app.marginPreferences.properties = {
         top:0, left:0, bottom:0, right:0,
         columnGutter:0, columnCount:1
         };
    var newDoc = app.documents.add({
        documentPreferences: {pageWidth:sb[3]-sb[1], pageHeight:sb[2]-sb[0]},
        });
    var mySelCopy = mySel.duplicate(newDoc.pages[0]);
    mySelCopy.move([0,0]);
    app.marginPreferences.properties = bkp;    
    writeFile = File.saveDialog( 'Save JPG as:' );
    app.jpegExportPreferences.jpegQuality = JPEGOptionsQuality.MAXIMUM;
    app.jpegExportPreferences.exportResolution = 300;
    newDoc.exportFile(ExportFormat.JPG, writeFile);
    newDoc.close(SaveOptions.no);
}