Deep maps an object's keys.

Creates an object with the same values as the provided object and keys generated by running the provided function for each key. Use Object.keys(obj) to iterate over the object's keys. Use Array.prototype.reduce() to create a new object with the same values and mapped keys using fn.

const deepMapKeys = (obj, f) =>
  Array.isArray(obj)
    ? obj.map(val => deepMapKeys(val, f))
    : typeof obj === 'object'
      ? Object.keys(obj).reduce((acc, current) => {
        const val = obj[current];
        acc[f(current)] =
          val !== null && typeof val === 'object' ? deepMapKeys(val, f) : (acc[f(current)] = val);
        return acc;
      }, {})
      : obj;

EXAMPLES

const obj = {
  foo: '1',
  nested: {
    child: {
      withArray: [
        {
          grandChild: ['hello']
        }
      ]
    }
  }
};
const upperKeysObj = deepMapKeys(obj, key => key.toUpperCase());
/*
{
  "FOO":"1",
  "NESTED":{
    "CHILD":{
      "WITHARRAY":[
        {
          "GRANDCHILD":[ 'hello' ]
        }
      ]
    }
  }
}
*/