mongo add collection size

size.js

db.getMongo().getDBNames().forEach(function(dbName) {
    if ("local" != dbName && "admin" != dbName && "system" != dbName) {
        var subject = db.getSiblingDB(dbName);
        subject.getCollectionNames().forEach(function (collectionName) {
            var stats = subject.runCommand({ collStats: collectionName, scale: 1024 * 1024 });
            print('Database: ' + dbName + ' - Collection: ' + collectionName + 
                  ' - Storage Size: ' + stats.storageSize + ' MB' +
                  ' - Free Storage Size: ' + stats.freeStorageSize + ' MB' +
                  ' - Total Index Size: ' + stats.totalIndexSize + ' MB' +
                  ' - Document Count: ' + stats.count +
                  ' - Avg Object Size: ' + stats.avgObjSize + ' bytes');
        });
    }
});