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const json1 = '{"hello":"world", "hi":"hello", "you":"me", "abc": "dfg"}';
const json2 = '{"hello":"world", "hi":"helloo", "you":"me", "abc": "123"}';

function getJSONDiff(json1, json2) {
  const different_keys = [];

  const objJSON1 = JSON.parse(json1);
  const objJSON2 = JSON.parse(json2);

  for (let key in objJSON1) {
    if (objJSON1[key] !== objJSON2[key]) {
      different_keys.push(key);
    }
  }
  different_keys.sort();

  return different_keys;
}

console.log(getJSONDiff(json1, json2));