Parse array of JSON object in JavaScript

Question

I have a JSON string:

{
    "country": "Mauritius",
    "provinces": [
        "mainland"
    ],
    "timeline": {
        "cases": {
            "3/19/20": 3,
            "3/20/20": 12,
            "3/21/20": 14,
            "3/22/20": 28,
            [...]
            "4/17/20": 324
        },
        "deaths": {
            "3/19/20": 0,
            "3/20/20": 0,
            "3/21/20": 1,
            "3/22/20": 2,
            [...]
            "4/17/20": 9
        },
        "recovered": {
            "3/19/20": 0,
            "3/20/20": 0,
            "3/21/20": 0,
            "3/22/20": 0,
            [...]
            "4/17/20": 108
        }
    }
}

What I want to achieve is to parse the value of cases, deaths and recovered into separate arrays in JavaScript.

For example, the number of cases, I want to find the difference in the number of cases from the previous date, with starting date as 3/19/20 within an initial cases of 3. I want to apply same logic for deaths and recovered. Hence, 3/20/20 should have a value of 9 (12 - 3)

Finally, I want to store each of this in arrays to use this data on a chart. Can someone please help me to parse this data in JavaScript or JQuery?

$.getJSON('https://corona.lmao.ninja/v2/historical/mauritius?lastdays=30', function(data) {

  let result = data.map(function(e) {
    return {
      cases: e.timeline.cases,
      deaths: e.timeline.deaths,
      recovered: e.timeline.recovered
    };
  }).reduce(function(acc, e) {

    Object.keys(e).forEach(function(t) {
      Object.keys(e[t]).forEach(function(d) {
        acc[t][d] = (acc[t][d] || 0) - e[t][d];
      });
    });
    return acc;
  }, {
    deaths: {},
    recovered: {},
    cases: {}
  });
  console.log(result)
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>

Answer 1

The following uses Array#reduce to transform the absolute values returned from the server, into the differences between days.

const entries = Object.entries, log = console.log, toJSON = JSON.stringify

const Δ = (arr, prev = 0) => 
  arr.reduce((acc, [date, curr]) => 
    (acc[date] = curr - prev, prev = curr, acc), {})
  
const AUTHORITY = 'corona.lmao.ninja'
async function fetchDeltas({ country, days = 30 }) {  
  const url = `//${AUTHORITY}/v2/historical/${country}?lastdays=${days}`
  const { timeline: { cases, deaths, recovered } } = await (await fetch(url)).json()
  return { 
    newCases: Δ(entries(cases)), 
    newDeaths: Δ(entries(deaths)),
    newRecoveries: Δ(entries(recovered))
  }
}
fetchDeltas({ country: 'mauritius' }).then(log)