fix issue #92

Value between rounded brackets for nth-child and nth-of-type pseudo-class gets purged if it starts with 'n' or '-n'

__tests__/purgecss.test.js

@@ -368,6 +368,18 @@ describe('pseudo selectors', () => {
         expect(purgecssResult.includes('some-item:nth-child(2n + 1)')).toBe(true)
     })
 
+    it('finds some-item:nth-of-type(n+3)', () => {
+        expect(purgecssResult.includes('some-item:nth-of-type(n+3)')).toBe(true)
+    })
+
+    it('finds some-item:nth-of-type(-1n+6)', () => {
+        expect(purgecssResult.includes('some-item:nth-of-type(-1n+6)')).toBe(true)
+    })
+
+    it('finds some-item:nth-of-type(-n+6)', () => {
+        expect(purgecssResult.includes('some-item:nth-of-type(-n+6)')).toBe(true)
+    })
+
     it('removes unused:only-child()', () => {
         expect(purgecssResult.includes('unused:only-child()')).toBe(false)
     })

__tests__/test_examples/pseudo_selector/pseudo_selector.css

@@ -6,6 +6,18 @@
   font-size: 1rem;
 }
 
+.some-item:nth-of-type(n+3) {
+  color: goldenrod;
+}
+
+.some-item:nth-of-type(-1n+6) {
+  color: brown;
+}
+
+.some-item:nth-of-type(-n+6) {
+  color: brown;
+}
+
 .unused:only-child() {
   color: red;
 }

src/index.js

@@ -305,7 +305,7 @@ class Purgecss {
                             selectorsInRule.push(value)
                         } else if (
                             type === 'tag' &&
-                            !/[+]|(even)|(odd)|^from$|^to$|^\d/.test(value)
+                            !/[+]|n|-|(even)|(odd)|^from$|^to$|^\d/.test(value)
                         ) {
                             // test if we do not have a pseudo class parameter (e.g. 2n in :nth-child(2n))
                             selectorsInRule.push(value)