Enforce explicitly comparing the `length` property of a value

Enforce explicitly checking the length of an object and enforce the comparison style.

This rule is fixable.

Zero comparisons

Enforce comparison with === 0 when checking for zero length.

if (!foo.length) {}

while (foo.length == 0) {}

do {} while (foo.length < 1);

if (; 0 === foo.length;) {}

const unicorn = 0 == foo.length ? 1 : 2;

if (1 > foo.length) {}

// Negative style is forbid too
if (!(foo.length > 0)) {}

if (foo.length === 0) {}

const unicorn = foo.length === 0 ? 1 : 2;

Enforce comparison with > 0 when checking for non-zero length.

if (foo.length !== 0) {}

while (foo.length != 0) {}

do {} while (foo.length >= 1);

for (; 0 !== foo.length; ) {}

const unicorn = 0 != foo.length ? 1 : 2;

if (0 < foo.length) {}

if (1 <= foo.length) {}

// Negative style is forbid too
if (!(foo.length === 0)) {}

if (foo.length > 0) {}

const unicorn = foo.length > 0 ? 1 : 2;

You can define your preferred way of checking non-zero length by providing a non-zero option (greater-than by default):

{
	'unicorn/explicit-length-check': [
		'error',
		{
			'non-zero': 'not-equal'
		}
	]
}

The non-zero option can be configured with one of the following:

greater-than (default)
- Enforces non-zero to be checked with: foo.length > 0
not-equal
- Enforces non-zero to be checked with: foo.length !== 0
greater-than-or-equal
- Enforces non-zero to be checked with: foo.length >= 1