Find first matching key

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'