Add attribute equality selectors

Author: eush77

README.md

@@ -31,7 +31,7 @@ select(ast, 'paragraph emphasis > text')
 - [x] Universal selector: `*`
 - [ ] Attribute selectors: `text[value*="substr"]`
   - [x] Existence: `[value]`
-  - [ ] Equality: `[value="foo"]`
+  - [x] Equality: `[value="foo"]`
   - [ ] Begins with: `[value^="prefix"]`
   - [ ] Containment: `[value*="substr"]`
   - [ ] Ends with: `[value$="suffix"]`

lib/select.js

@@ -40,7 +40,7 @@ select.rule = function (selector, ast) {
       break;
 
     default:
-      throw Error('Unexpected nesting operator: ' + selector.nestingOperator);
+      throw Error('Undefined nesting operator: ' + selector.nestingOperator);
   }
 
   return result;
@@ -85,7 +85,30 @@ function matches (rule, node) {
 
   // Match attributes.
   return (rule.attrs || []).every(function (attr) {
-    return attr.name in node;
+    switch (attr.operator) {
+      case undefined:
+        return attr.name in node;
+
+      case '=':
+        // First, check for special values.
+        switch (attr.value) {
+          case 'null':
+            if (attr.name in node && node[attr.name] == null) return true;
+            break;
+
+          case 'true':
+            if (node[attr.name] === true) return true;
+            break;
+
+          case 'false':
+            if (node[attr.name] === false) return true;
+            break;
+        }
+        return node[attr.name] == attr.value;
+
+      default:
+        throw Error('Undefined attribute operator: ' + attr.operator);
+    }
   });
 }
 

test/test.js

@@ -102,7 +102,20 @@ test('universal selector', function (t) {
 
 
 test('attribute selectors', function (t) {
+  t.comment('existence');
   t.deepEqual(select(ast, '[depth]'), select(ast, 'heading'));
   t.deepEqual(select(ast, '[start][ordered]'), select(ast, 'list'));
+
+  t.comment('equality');
+  t.deepEqual(select(ast, 'heading[depth=1], [depth=3]'), [
+    path(ast, [0]),
+    path(ast, [7])
+  ]);
+  t.deepEqual(select(ast, 'paragraph [type="text"]'),
+              select(ast, 'paragraph text'));
+  t.deepEqual(select(ast, '[start=null]'), select(ast, 'list').slice(0, 3));
+  t.deepEqual(select(ast, '[ordered=true]'), [ast.children[6]]);
+  t.deepEqual(select(ast, 'list[loose=false]'), select(ast, 'list'));
+
   t.end();
 });