class Migrator { constructor (opts = {}) { const migrations = opts.migrations || [] // sort migrations by version this.migrations = migrations.sort((a, b) => a.version - b.version) // grab migration with highest version const lastMigration = this.migrations.slice(-1)[0] // use specified defaultVersion or highest migration version this.defaultVersion = opts.defaultVersion || (lastMigration && lastMigration.version) || 0 } // run all pending migrations on meta in place async migrateData (versionedData = this.generateInitialState()) { const pendingMigrations = this.migrations.filter(migrationIsPending) for (let index in pendingMigrations) { let migration = pendingMigrations[index] versionedData = await migration.migrate(versionedData) if (!versionedData.data) throw new Error('Migrator - migration returned empty data') if (versionedData.version !== undefined && versionedData.meta.version !== migration.version) throw new Error('Migrator - Migration did not update version number correctly') } return versionedData // migration is "pending" if it has a higher // version number than currentVersion function migrationIsPending (migration) { return migration.version > versionedData.meta.version } } generateInitialState (initState) { return { meta: { version: this.defaultVersion, }, data: initState, } } } module.exports = Migrator