Standard allows certain unnecessary semicolons

[dcposch]

Version: 8.6.0

Example 1: reports the unnecessary semicolon

module.exports = function Foo () {
};

Example 2: no error

module.exports = Foo
function Foo () {
};

Example 3: no error

;
;
module.exports = Foo
function Foo () {
};
;
;

[dcposch]

Is this on purpose?

Otherwise, are we missing an eslint rule?

[feross]

We're missing an eslint rule: no-extra-semi.

We used to enable this, but it was relaxed in 3.1.2. Context here: #70

Options are:

1. Re-enable the rule, though it means that in some circumstances users will need to break the rule "Don't ever start a line with ( or [".

2. Keep it disabled

3. See if ESLint would accept a PR that adds an option to the rule to ignore extra semis when they precede a specified whitelist of characters. We would include the full list of ASI gotcha characters: [, (, +, *, /, -, ,, .

[dcposch]

i vote #1

though it means that in some circumstances users will need to break the rule

i think it means they have to follow that rule, right?

[feross]

@dcposch If you have an immediately executing function like this:

;(function () {
  console.log('hey')
})()

It's common to put a semi in front, in case there's something before it that fails with ASI. Here's an example where the semi is required to get the correct behavior:

console.log('hi')
;(function () { // without the semi, this is interpreted as a function invocation
  console.log('hey')
})()

However, there are certain things that could come before that don't actually require a semi:

if (x) {
  console.log('hi')
}
;(function () { // this semi is technically NOT required
  console.log('hey')
})()

If-blocks don't actually require a semi after them, since there's no way the paren that follows could be a function invocation. That said, it's a good idea to just always put in a semi before ( and [. The problem is that no-extra-semi will warn about this last case, forcing the user to remove it.

if (x) {
  console.log('hi')
}
(function () { // this is perfectly safe, though it doesn't look like it
  console.log('hey')
})()

[tunnckoCore]

So we should go back to use semicolons everywhere! 😱 Haha, just a joke.

I'm for 1 too.

The problem is that no-extra-semi will warn about this last case, forcing the user to remove it.

There's autofix and everyone should use it. The autofix will remove it in that last case, but won't remove it in the example with console.log

console.log('hi')
;(function () { // without the semi, this is interpreted as a function invocation
  console.log('hey')
})()

Above is confirmed.

So I don't see any problems.

[indiesquidge]

I don't know if this should count as part of this thread or opened as a new issue (or if this case is even supported at all since it requires the babel-eslint parser), but I have the same issue of Standard allowing semicolons for ES class fields and static properties

export class Bork {
  // Property initializer syntax
  instanceProperty = 'bork';
  boundFunction = () => {
    return this.instanceProperty
  };

  // Static class properties
  static staticProperty = 'babelIsCool';
  static staticFunction = function () {
    return Bork.staticProperty
  };
};

// standard does not complain about these semicolons.

[stale]

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