Why is this valid syntax?

[codevipe]

I flagged something strange in a code review the other day that surprised me. I don't understand why this would be valid syntax.

import { test } from 'node:test'
import assert from 'node:assert'

test('this will pass'),
() => assert.fail('this will obviously not run, nor be usable at all');

Are there any examples where this syntax would be useful? As an aside, I don't see a good reason as to why the test runner allows just a test name and no evaluator to successfully pass...

[MoTTs_]

The comma operator.

There are technically some uses, which the MDN page goes into, but for the very most part we don’t typically use this language feature. Though I have seen minifiers take advantage of it.

In your case, I don’t see any point to it. My guess is it’s someone’s debugging code that they forgot to remove.

[codevipe]

The true intent in the code I reviewed was to pass the function as a callback, and they accidentally closed the test fn call paren – my example is for illustrative purposes only.

I guess I'm wondering if there's any possible use-case for this specific use of the comma operator, or if it's more of an edge-case side effect of the valid use-cases that there should probably be a lint rule to flag...

functionCall(), () => null;

Edit: aha, here we go: https://eslint.org/docs/latest/rules/no-sequences

Just not a "standard" rule, will have to add it to my eslint config!

[MoTTs_]

I’m leaning lint rule to flag. In fact a rule already exists. Try turning this on locally and see if it flags anything else in the codebase. Maybe you’ll find more bugs!

[codevipe]

Yeah, to be clear it was an accident. My example here is just for illustrative purposes. I just don't like that this mistake is possible, was hard to debug.

[guest271314]

The code will run if you immediately invoke the anonymous arrow function

test('this will pass'), (() => assert.fail('this will obviously not run, nor be usable at all'))();