sequelize/sequelize · error · Error

Migration ${inspect(migrationName)} has an invalid "down" ex

Error message

Migration ${inspect(migrationName)} has an invalid "down" export: It must be a function, but it is ${inspect(down)}

What it means

createJsMigration located a `down` export but `isFunction(down)` is false. Since `down` is invoked as a function to revert the migration, a non-callable value is rejected.

Source

Thrown at packages/cli/src/api/get-umzug.ts:162

        );
      }

      const sequelize = migrationParams.context.sequelize;

      await up(sequelize.queryInterface, sequelize, migrationParams);
    },
    down: async migrationParams => {
      const migration = await import(pathToFileURL(migrationPath).href);
      const down = migration.down ?? migration.default?.down;

      if (!down) {
        throw new Error(
          `Migration ${inspect(migrationName)} is missing the "down" export, so cannot be reverted.`,
        );
      }

      if (!isFunction(down)) {
        throw new Error(
          `Migration ${inspect(migrationName)} has an invalid "down" export: It must be a function, but it is ${inspect(down)}`,
        );
      }

      const sequelize = migrationParams.context.sequelize;

      await down(sequelize.queryInterface, sequelize, migrationParams);
    },
  };
}

View on GitHub (pinned to 7e1deec499)

Solutions

Make `down` a function: `export async function down(queryInterface) { ... }`.
If irreversibility is intended, omit `down` entirely (you will get error [7] on undo instead) and simply never undo it.

Example fix

// before
export const down = null;
// after
export async function down(queryInterface) { await queryInterface.dropTable('users'); }

Defensive patterns

Strategy: type-guard

Validate before calling

function assertDownIsFunction(mod: any, file: string) {
  const down = mod.down ?? mod.default?.down;
  if (typeof down !== 'function') {
    throw new Error(`'down' in ${file} must be a function, got ${typeof down}`);
  }
}

Type guard

function isMigrationDown(mod: any): mod is { down: (...a: any[]) => any } {
  return typeof mod?.down === 'function' || typeof mod?.default?.down === 'function';
}

Prevention

Never assign non-function values to `down`; if irreversible, omit `down` and avoid undoing it.
Run a CI check asserting `down` is a function for every migration file.

When it happens

Trigger: Exporting `down` as a non-function — an object, string, or constant — in a JS migration that is then reverted.

Common situations: Placeholder `export const down = null`/`false`; copying a config object into `down`; refactor leftover.

Related errors

AI-assisted analysis of sequelize/sequelize@7e1deec499 (2026-08-03). Data as JSON: /data/errors/201f22fca739ab70.json. Report an issue: GitHub.