Find last matching key

OSCC · JavaScript, Object · Oct 22, 2020

Finds the last key that satisfies the provided testing function. Otherwise undefined is returned.

  • Use Object.keys() to get all the properties of the object.
  • Use Array.prototype.reverse() to reverse the order and Array.prototype.find() to test the provided function for each key-value pair.
  • The callback receives three arguments - the value, the key and the object.
const findLastKey = (obj, fn) =>
  Object.keys(obj)
    .reverse()
    .find(key => fn(obj[key], key, obj));
findLastKey(
  {
    barney: { age: 36, active: true },
    fred: { age: 40, active: false },
    pebbles: { age: 1, active: true }
  },
  x => x['active']
); // 'pebbles'

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