If you're arriving here as a express-validator v3 user after upgrading to v4+, please check the upgrade guide in order to find out what's different!
Also please note that, starting with v5.0.0, no new features will be accepted into the legacy API. Only bug fixes will be made.
npm install express-validator
Also make sure that you have Node.js 6 or newer in order to use it.
Please refer to the documentation website on https://express-validator.github.io.
Check the GitHub Releases page.