Compact all collections inside of a MongoDB database

compact.js

// This script loops though the list of collection names in a MongoDB and runs the compact operation on them
// Simply paste this into the Mongo shell

use testDbName;
db.getCollectionNames().forEach(function (collectionName) {
    print('Compacting: ' + collectionName);
    db.runCommand({ compact: collectionName });
});

db.getCollectionNames returns views too 🙃

Returns an array containing the names of all collections and views

https://www.mongodb.com/docs/manual/reference/method/db.getCollectionNames/

If you want collection names only you need something like db.getCollectionInfos({ type: 'collection' }).map(v => v.name).filter(v => v != 'system.views')