add :nth-last-child

Author: eush77

README.md

@@ -62,7 +62,7 @@ That's it!
 - [ ] Structural pseudo-classes: `paragraph:first-of-type`
   - [x] `:root`
   - [x] `:nth-child(2n+1)`
-  - [ ] `:nth-last-child(2n+1)`
+  - [x] `:nth-last-child(2n+1)`
   - [ ] `:nth-of-type(2n+1)`
   - [ ] `:nth-last-of-type(2n+1)`
   - [x] `:first-child`

lib/match-node.js

@@ -67,6 +67,9 @@ function matchPseudos (rule, node, nodeIndex, parent) {
       case 'nth-child':
         return parent && pseudo.value(nodeIndex);
 
+      case 'nth-last-child':
+        return parent && pseudo.value(parent.children.length - 1 - nodeIndex);
+
       case 'first-child':
         return parent && nodeIndex == 0;
 

lib/selector.js

@@ -30,7 +30,7 @@ function compileNthChecks (ast) {
     case 'rule':
       if (ast.pseudos) {
         ast.pseudos.forEach(function (pseudo) {
-          if (pseudo.name == 'nth-child') {
+          if (pseudo.name == 'nth-child' || pseudo.name == 'nth-last-child') {
             pseudo.value = nthCheck(pseudo.value);
             pseudo.valueType = 'function';
           }

test/select.js

@@ -155,6 +155,22 @@ test('structural pseudo-classes', function (t) {
     t.end();
   });
 
+  t.test(':nth-last-child', function (t) {
+    t.deepEqual(select(ast, ':root:nth-last-child(n)'), []);
+    t.deepEqual(select(ast, 'tableCell:nth-last-child(-n+2)'), [
+      path(ast, [10, 0, 1]),
+      path(ast, [10, 0, 2]),
+      path(ast, [10, 1, 1]),
+      path(ast, [10, 1, 2]),
+      path(ast, [10, 2, 1]),
+      path(ast, [10, 2, 2])
+    ]);
+    t.deepEqual(select(ast, 'definition:nth-last-child(odd)')
+                .map(function (node) { return node.identifier }),
+                ['viverra', 'interdum']);
+    t.end();
+  });
+
   t.test(':first-child', function (t) {
     t.deepEqual(select(ast, ':root:first-child'), []);
     t.deepEqual(select(ast, 'heading:first-child'), [path(ast, [0])]);