Add support for the Option Chaining (`?.`) operator

[MeGaGiGaGon]

Issue type:

• ➕ Feature request

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Short description:

The optional chaining operator allows for short-circuiting operations instead of crashing on undefined values. This is very useful with functions that can return undefined, for example targetBlock on entities.

In this code

if (player.targetBlock().mod() == "Pipez") {}

If the player isn't looking at a block, the script will crash with a ".mod is not a property of undefined" error. The code I often use to fix this is

if (player.targetBlock() != undefined && player.targetBlock().mod() == "Pipez") {}

TypeScript does not accept this since it gives a race condition where the block might have changed. The correct way is something like

var _temp = player.targetBlock();
if (_temp != undefined && _temp.mod() == "Pipez") {}

With the TypeScript ?. replacement generated code when targeting es2019 or earlier being

var _a;
if (((_a = player.targetBlock()) === null || _a === void 0 ? void 0 : _a.mod()) == "Pipez") {}

Comparing all of this to if ?. was available:

if (player.targetBlock()?.mod() == "Pipez") {}

It's clear that this would be a massive win for ease of use and readability. I am unsure what effect it would have on performance.

If this is impossible to add due to the backend, then the manual should be updated, as it says:

All features allowed by ECMAScript (ECMA-262) are available.

But does not specify which version of ECMAScript (ECMA-262) is available, with ?. having been added in version 10.0

[rubensworks]

Thanks for the suggestion!

[rubensworks]

Hmm, optional chaining should be present in GraalJS since V20.1.0, and we're already at V24, so this should be working...
Maybe a config option somewhere in GraalJS.

[MeGaGiGaGon]

Hm, I tried to reproduce again now that I have Minecraft access again, but could not get a reproduction. I think what happened was that since I tried this first when I was still newer to using scripting, I got one of the errors that happens when you need to refresh the variable cards, changed my script back, and it worked, so I assumed ?. didn't work when it should have, so false alarm; sorry for the churn.
(Though I do still think the docs should be updated to say the supported version of ECMAScript , since if it had clearly said a version > 10.0 I would have at least of time of writing this issue found my error, or at some point prior)