capitalize-json-keys-recursevely.js

let obj = {
  "name": "john",
  "Age": "21",
  "sex": "male",
  "place": {"state": "ca"},
  "cats": [{"name": "toby"}, {"name": "wiskers"}]
};

let capitalize = (s) => {
  if (typeof s !== 'string') return '';
  return s.charAt(0).toUpperCase() + s.slice(1);
};


let allKeysToCapCase = (obj) => {
  let output = {};
  for (i in obj) {
    if (Object.prototype.toString.apply(obj[i]) === '[object Object]') {
      output[capitalize(i)] = allKeysToCapCase(obj[i]);
    } else if (Object.prototype.toString.apply(obj[i]) === '[object Array]') {
      output[capitalize(i)] = obj[i].map(x => allKeysToCapCase(x));
    } else {
      output[capitalize(i)] = obj[i];
    }
  }
  return output;
};

let o = allKeysToCapCase(obj);
// {"Name":"john","Age":"21","Sex":"male","Place":{"State":"ca"},"Cats":[{"Name":"toby"},{"Name":"wiskers"}]}
JSON.stringify(o);