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decoders

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  • License MIT

Elm-like decoders for when working with Flow types in JS

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  • decoders

This package does not declare an exports field, so the exports above have been automatically detected and optimized by JSPM instead. If any package subpath is missing, it is recommended to post an issue to the original package (decoders) to support the "exports" field. If that is not possible, create a JSPM override to customize the exports field for this package.

Readme

decoders

Elm-like decoders for use with Flow in JS.

See http://elmplayground.com/decoding-json-in-elm-1 for an introduction.

Why?

All JSON responses coming from our API endpoints are just that: free-form JSON data. To Flow, the only type classification possilbe is "any" -- effectively turning off all type checks for anything related to JSON. To the receiving end (our frontend), the structure of that data is completely opaque to any type checkers since JSON values can be anything: an object, an array, null, a string, a bool, etc. Our type system is not a runtime type system, so we need a way of "converting" an any-type JSON value into a type that we want to work with in our frontend code base.

Elm's solution to this problem is to define composable decoders: functions that take anything and either fail with an error, or guarantee to return the expected type. In our case, it's fine to fail with a runtime error.

For example a string decoder will:

decodeString('ohai')      => 'ohai'
decodeString(false)       => RUNTIME ERROR
decodeString({foo: 123})  => RUNTIME ERROR
decodeString(null)        => RUNTIME ERROR