Find first matching key

OSCC · JavaScript, Object · Oct 22, 2020

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

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

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