undefined
is returned.Object.keys(obj)
to get all the properties of the object.Array.prototype.reverse()
to reverse the order and Array.prototype.find()
to test the provided function for each key-value pair.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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