Enforce using the separator argument with `Array#join()`

✅ This rule is part of the recommended config.

🔧 This rule is auto-fixable.

It's better to make it clear what the separator is when calling Array#join(), instead of relying on the default comma (',') separator.

Fail

const string = array.join();

const string = Array.prototype.join.call(arrayLike);

const string = [].join.call(arrayLike);

const string = array.join(',');

const string = array.join('|');

const string = Array.prototype.join.call(arrayLike, '');

const string = [].join.call(arrayLike, '\n');