Add memo cache to improve performance of repeated parse calls

esquery.js

@@ -1,13 +1,14 @@
 /* vim: set sw=4 sts=4 : */
 (function () {
-
     var estraverse = require('estraverse');
     var parser = require('./parser');
 
     var isArray = Array.isArray || function isArray(array) {
         return {}.toString.call(array) === '[object Array]';
     };
 
+    var PARSE_CACHE = {};
+
     var LEFT_SIDE = {};
     var RIGHT_SIDE = {};
 
@@ -312,7 +313,12 @@
          * Parse a selector string and return its AST.
          */
         function parse(selector) {
-            return parser.parse(selector);
+            if (PARSE_CACHE[selector]) {
+                return PARSE_CACHE[selector];
+            }
+            var parsed = parser.parse(selector);
+            PARSE_CACHE[selector] = parsed;
+            return parsed;
         }
 
         /**

tests/parser.js

@@ -1,7 +1,7 @@
 define([
     "esquery",
     "jstestr/assert",
-    "jstestr/test",
+    "jstestr/test"
 ], function (esquery, assert, test) {
 
     test.defineSuite("basic query parsing", {
@@ -18,7 +18,11 @@ define([
             assert.isNotEqual(void 0, esquery.parse("A     "));
             assert.isNotEqual(void 0, esquery.parse(" A "));
             assert.isNotEqual(void 0, esquery.parse("     A     "));
-        }
+        },
 
+        "memoize selector parsing": function () {
+            assert.isEqual(JSON.stringify(esquery.parse("A")) === JSON.stringify(esquery.parse("A")), true);
+            assert.isEqual(esquery.parse("A") === esquery.parse("A"), true);
+        }
     });
 });