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bahmutov/index.js

Created August 10, 2017 15:37
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  1. bahmutov created this gist Aug 10, 2017.
    49 changes: 49 additions & 0 deletions index.js
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    // following along https://medium.com/@luijar/kliesli-compositions-in-javascript-7e1a7218f0c4
    const R = require('ramda')
    const Maybe = require('ramda-fantasy').Maybe

    // parse JSON string into object
    // parse :: String -> Object | Null
    function parse(s) {
    try {
    return JSON.parse(s)
    } catch (e) {
    return null
    }
    }

    // prop :: (Object, String) -> Object | String | Null
    const prop = (obj, name) => obj[name]

    // maybeParseJson :: String -> Maybe
    const maybeParseJson = json => Maybe.toMaybe(parse(json))

    // maybeProp :: String -> Object -> Maybe
    const maybeProp = prop => obj => Maybe.toMaybe(obj[prop])

    // convert a "simple" function to return Maybe
    // https://github.com/ramda/ramda-fantasy/blob/master/docs/Maybe.md#maybeof
    const maybeUpper = R.compose(Maybe.of, R.toUpper)

    // a typical user object is
    /*
    {
    user:
    {
    address:
    {
    state: "fl"
    }
    }
    }
    */
    // getStateCode :: String -> Maybe
    const getStateCode = R.composeK(
    maybeUpper,
    maybeProp('state'),
    maybeProp('address'),
    maybeProp('user'),
    maybeParseJson
    )

    module.exports = getStateCode
    22 changes: 22 additions & 0 deletions spec.js
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    // testing getStateCode
    const getStateCode = require('./index')

    it('extracts from valid string', () => {
    const s = '{"user": {"address": {"state": "in"}}}'
    const state = getStateCode(s).getOrElse('an error')
    console.assert(state === 'IN', state)
    })

    it('handles invalid JSON string', () => {
    // notice missing quotes
    const s = '{"user": {"address": {state: in}}}'
    const state = getStateCode(s).getOrElse('an error')
    console.assert(state === 'an error', state)
    })

    it('handles missing property', () => {
    // notice missing address
    const s = '{"user": {}}'
    const state = getStateCode(s).getOrElse('an error')
    console.assert(state === 'an error', state)
    })