findKeys

Finds all the keys in the provided object that match the given value.

• Use Object.keys(obj) to get all the properties of the object.
• Use Array.prototype.filter() to test each key-value pair and return all keys that are equal to the given value.

const findKeys = (obj, val) => 
  Object.keys(obj).filter(key => obj[key] === val);

const ages = {
  Leo: 20,
  Zoey: 21,
  Jane: 20,
};
findKeys(ages, 20); // [ 'Leo', 'Jane' ]