"singleGroups" option gives spurious warnings for negative instanceof condition

[Qantas94Heavy]

Using JSHint v2.5.11, when I try the following code:

// jshint singleGroups:true
if (!(a instanceof b)) alert(1);

It will give out a spurious warning that "Grouping operator is unnecessary for lone expressions". It is in fact necessary, because the unary negation operator has a higher precedence than the instanceof operator.

[rwaldron]

The "ES6" label was a finger slip, sorry about that.

[jugglinmike]

This is also the case for the in operator. I've opened gh-2065 to address the bug.

[Krinkle]

Should we exclude !! (boolean cast) as well?

      4 |return !!( window.JSON && JSON.stringify && JSON.parse );
                                                                 ^ Grouping operator is unnecessary for lone expressions.

[rwaldron]

Grouping operator is unnecessary for lone expressions

In the example you gave, this error just seems wrong.

[jugglinmike]

@Krinkle Definitely. @rwaldron is right, that is another bug. It's covered by my patch in gh-2065, but I've added another regression test to be safe. Thanks!

[gagle]

Same issue here:

//Warning
path.resolve(alias.dir, alias.path) + (obj.trail ? '/' + obj.trail : '');

//No warning & invalid
path.resolve(alias.dir, alias.path) + obj.trail ? '/' + obj.trail : '';
//Same as
(path.resolve(alias.dir, alias.path) + obj.trail) ? '/' + obj.trail : '';

[dsl101]

Another example?

var a = 2;
var b = 3;
var resultStr;

// Correct answer (5), but jshint gives warning:
resultStr = 'Total: ' + (a + b) + '.';
                                ^ Grouping operator is unnecessary for lone expressions.

// Incorrect answer (23), but jshint gives no warning:
resultStr = 'Total: ' + a + b + '.';

[Qantas94Heavy]

Also, should this trigger the warning or not?

// jshint singleGroups:true
if ( (foo = 1) ) alert(1);

This is usually used to indicate that the assignment was deliberate, but currently triggers a warning with the singleGroups option enabled even though adding the parentheses silences the "assignment instead of conditional expression" warning.

[gagle]

I still receive the warning:

Warning & valid

> 'foo' + ('bar' ? 'baz' : 'qux');
foobaz

No warning & invalid

> 'foo' + 'bar' ? 'baz' : 'qux';
baz