Flow also supports "discriminated unions" [0], and did so before TypeScript (Flow's announcement in July 2015: https://flow.org/blog/2015/07/03/Disjoint-Unions/

Flow also supports "discriminated unions" [0], and did so before TypeScript (Flow's announcement in July 2015: https://flow.org/blog/2015/07/03/Disjoint-Unions/ https://flow.org/blog/2015/07/03/Disjoint-Unions/, TypeScript's announcement in August 2016: https://devblogs.microsoft.com/typescript/announcing-typescript-2-0-rc-2/ https://devblogs.microsoft.com/typescript/announcing-typescr...), though it doesn't yet support destructuring the "kind" field as was just added to TypeScript. [0] https://flow.org/try/#0C4TwDgpgBAggxsAlgewHZQLwCgq6gHygG8oBrRVAEwC4oByGOgGijAEMQAbZNmqVAK4BbAEYQATlAC+OPIRLkqtOgCFmrDt160AzsHEUA5tIDcWLADMBqBCnQWAjAAYAFG1tpa8JGgCUxWVxECyg3D1QAOkVKTAwMekZ-IkC8XHcfSPYuHkoI4GQAMUQADwhKF18zVJlU4ND0uyiKGLj41ToklNSGtAisrVz8gFUwSHEAYTYdCAqqvBkZS2twqEcHMIyvcM7akI3G6Ni2xIDU1Lg0PWJ+nKlMKB7UObONbN48wpKy2ZSavDr9r1Dq16Godi8oBdUFciDdeHd4o9nmc4YNkCMxpNpj9qlhFlYbBlVg4AEyA1BbDLg3A6ADuiGAcAAFvVwk0qNSznAptAGHRqF0IY8+poch8iqVypVBS8ROIIGxSMjzjzQfyZWdhaiPhiJFiZtKIWc5QqlRrKBALGwBJxgAKjd02aiTLgAPSu-gQABuEl+eKAA https://flow.org/try/#0C4TwDgpgBAggxsAlgewHZQLwCgq6gHygG8oBr...