Fix using negative value in step (#3)

index.js

@@ -4,6 +4,9 @@ const validate = (name, value) => {
 	}
 };
 
+const lt = (l, r) => l < r;
+const gt = (l, r) => l > r;
+
 export default function * getRange({start = 0, end, step = 1}) {
 	if (step === 0) {
 		throw new TypeError('The `step` parameter cannot be zero');
@@ -13,7 +16,9 @@ export default function * getRange({start = 0, end, step = 1}) {
 	validate('end', end);
 	validate('step', step);
 
-	for (let index = start; index < end; index += step) {
+	const compare = step < 0 ? gt : lt;
+
+	for (let index = start; compare(index, end); index += step) {
 		yield index;
 	}
 }

test.js

@@ -20,6 +20,17 @@ test('main', t => {
 	t.deepEqual(get({start: 0, end: 3, step: 2}), [0, 2]);
 	t.deepEqual(get({start: 0, end: 4, step: 2}), [0, 2]);
 	t.deepEqual(get({start: 0, end: 6, step: 2}), [0, 2, 4]);
+
+	t.deepEqual(get({start: 0, end: -1, step: -1}), [0]);
+	t.deepEqual(get({start: 0, end: -2, step: -1}), [0, -1]);
+	t.deepEqual(get({start: -1, end: -2, step: -1}), [-1]);
+	t.deepEqual(get({start: -1, end: -5, step: -1}), [-1, -2, -3, -4]);
+	t.deepEqual(get({start: 2, end: -2, step: -1}), [2, 1, 0, -1]);
+
+	t.deepEqual(get({start: 0, end: -2, step: -2}), [0]);
+	t.deepEqual(get({start: 0, end: -3, step: -2}), [0, -2]);
+	t.deepEqual(get({start: 0, end: -4, step: -2}), [0, -2]);
+	t.deepEqual(get({start: 0, end: -6, step: -2}), [0, -2, -4]);
 });
 
 test('generator', t => {