Add attribute existence selectors

Author: eush77

README.md

@@ -30,7 +30,7 @@ select(ast, 'paragraph emphasis > text')
 - [x] Group selectors: `paragraph, text`
 - [x] Universal selector: `*`
 - [ ] Attribute selectors: `text[value*="substr"]`
-  - [ ] Existence: `[value]`
+  - [x] Existence: `[value]`
   - [ ] Equality: `[value="foo"]`
   - [ ] Begins with: `[value^="prefix"]`
   - [ ] Containment: `[value*="substr"]`

lib/select.js

@@ -46,7 +46,7 @@ select.rule = function (selector, ast) {
   return result;
 
   function walk (node, parent) {
-    if (selector.tagName == '*' || node.type == selector.tagName) {
+    if (matches(selector, node)) {
       if (!selector.rule) {
         append(result, [node]);
       }
@@ -76,6 +76,20 @@ select.rule = function (selector, ast) {
 };
 
 
+// True if node matches head of selector rule.
+function matches (rule, node) {
+  // Match type.
+  if (rule.tagName && rule.tagName != '*' && node.type != rule.tagName) {
+    return false;
+  }
+
+  // Match attributes.
+  return (rule.attrs || []).every(function (attr) {
+    return attr.name in node;
+  });
+}
+
+
 function append (array, elements) {
   elements.forEach(function (el) {
     if (array.indexOf(el) < 0) {

test/test.js

@@ -99,3 +99,10 @@ test('universal selector', function (t) {
     }, 0);
   }
 });
+
+
+test('attribute selectors', function (t) {
+  t.deepEqual(select(ast, '[depth]'), select(ast, 'heading'));
+  t.deepEqual(select(ast, '[start][ordered]'), select(ast, 'list'));
+  t.end();
+});