2022 has come to an end, and this year saw the release of the ES2022 spec which included lots of new features in Javascript. I wanted to take some time to

1. share my most used subset of these, and
2. talk about some the most exciting Stage 3 proposals I’ve read

Array.findLast()

findLast joins the commonly used map | reduce | filter and friends of Array. The function makes it easy to find the last element of an Array that matches a given criteria.

const array1 = [5, 12, 50, 130, 44];
const found = array1.findLast((element) => element > 45);
console.log(found); // 130

Error cause field

Oftentimes, we catch an error returned by a downstream function and want to throw a more informative error. But if we overwrite the message on an Error object, we lose the underlying cause of the error itself. So we have a better error message (+) that’s harder to debug (-).

The cause field allows us to propagate errors upstream, giving us the best of both worlds: better error messages (+) that are easier to debug (+)

try {
  connectToDatabase();
} catch (err) {
  throw new Error('Connecting to database failed.', { cause: err });
}

Object.hasOwn()

If you’ve wanted to check if an object has a given property, you’ve probably reached for Object.hasOwnProperty() However, this function doesn’t behave as expected in some scenarios, for example when using Object.create to create a copy of an object.

This is just one example, read more in the ECMAScript Proposal:

const object1 = { hello: "world" };
console.log(object1.hasOwnProperty("hello")); // true

const object2 = Object.create(object1);
console.log(object2.hasOwnProperty("hello")); // false

// However:
object2.hasOwn("hello") // true

Regexp Match Indices

Match Indices are meant to provide a list of indices at which a given string matches a given regular expression. Prior to this proposal, regexp.match(string) would return an index field, but it would only correlate to the first index which matched the regular expression.

NOTE: For performance reasons, indices will only be added to the result if the d flag is specified.

const str = "foo bar foo";
const regexp = /foo/dg;
// The `indices` field is returned if the `d`
// modifier is present on the regex
console.log(regexp.exec(str).indices[0]); // [0, 3]

The Future

2022 was a big year for Javascript, but we have some even cooler stuff coming soon. Here are some of them which I’m particularly excited about! (You can track ECMAScript Proposals as proposals.es)