Model Promise immutability [flow] property `username` (user.js:20:7) Covariant property `username` incompatible with contravariant use in assignment of property `username`
https://github.com/flowtype/flow-typed flow-typed install Third Party https://github.com/facebook/immutable-js/blob/master/type -definitions/immutable.js.flow Finally, Immutable.js supports Flow type in v4.0.0-rc1
Compare Typescript if you use Flow, you'll have much higher type coverage much faster and you'll be able to sleep soundly. http://thejameskyle.com/adopting-flow-and-typescript.html
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