Iterate over a JavaScript object's own properties

Array.prototype.forEach() is a great way to iterate over an array, but it doesn't work for objects. However, with a little help from Object.keys(), we can easily create our own object property iterator.

Iterate over object properties

As mentioned already, we simply need to use Object.keys() to get all the properties of the object and then use Array.prototype.forEach() to run the provided function for each key-value pair. The callback should receive three arguments - the value, the key and the object itself.

const forOwn = (obj, fn) =>
  Object.keys(obj).forEach(key => fn(obj[key], key, obj));

forOwn({ foo: 'bar', a: 1 }, v => console.log(v));
// Logs: 'bar', 1

Iterate over object properties in reverse

If you need to iterate over the object properties in reverse, you can use Array.prototype.reverse() to reverse the order of the keys before iterating over them.

const forOwnRight = (obj, fn) =>
  Object.keys(obj)
    .reverse()
    .forEach(key => fn(obj[key], key, obj));

forOwnRight({ foo: 'bar', a: 1 }, v => console.log(v));
// Logs: 1, 'bar'