Best Features of ES2019 — Catch, Sort, and toString

Since 2015, JavaScript has improved immensely.

It’s much more pleasant to use it now than ever.

In this article, we’ll look at the best features of ES2019.

Catch Binding

catch binding is now optional with ES2019.

For instance, we can write:

let jsonData;
try {
  jsonData = JSON.parse(str);
} catch {
  jsonData = {};
}

Then we don’t need to get the thrown object in the parentheses after the catch .

However, other kinds of errors that aren’t related to parsing will be silently ignored, since we just set it the jsonData object to an empty object.

Another example would be to get a deeply nested property.

For instance, we can just write:

function logId(item) {
  let id;
  try {
    id = item.data.id;
  } catch {
    console.log(id);
  }
}

to let us safely get the deeply nested id property of item to id if it exists.

If it doesn’t exist, then the code in the catch block is run.

Stable Array.prototype.sort()

The Array.prototype.sort method is now guaranteed to be stable.

So if something is considered to be the same when sorting, then they’ll stay in the same order in engines that supports ES2019.

If we have:

const arr = [{
    key: 'foo',
    value: 1
  },
  {
    key: 'bar',
    value: 2
  },
  {
    key: 'foo',
    value: 3
  },
];
arr.sort((x, y) => x.key.localeCompare(y.key, 'en'));

Then arr would be in the same order regardless of which environment it’s in.

JSON.stringify

JSON.stringify can now take a lone surrogate.

So if we have:

JSON.stringify('u{D800}')

Then we get:

""ud800""

JSON superset

JSON strings now can have the '"u2028"' character.

Function.prototype.toString Changes

Function.prototype.toString now has some changes since ES2019.

The functions we defined returns a string with the original source code.

If we call toString with a built-in function, then we see [native code] .

For instance, if we have:

isNaN.toString()

Then we get:

"function isNaN() { [native code] }"

Functions created dynamically with the Function and GeneratorFunction engines must create the appropriate source code and attach it to functions.

All other cases would throw a type error.

Conclusion

Catch binding, function toString , sort methods all have changes with ES2019.