assert: improve deepEqual perf for large input

Use a Map instead of an array for checking previously found cyclic references. This reduces complexity for an array-of-objects case from O(n²) to O(n·log n). Fixes: nodejs#12842 PR-URL: nodejs#12849 Reviewed-By: Colin Ihrig <[email protected]> Reviewed-By: Joyee Cheung <[email protected]> Reviewed-By: James M Snell <[email protected]> Reviewed-By: Jeremiah Senkpiel <[email protected]> Reviewed-By: Refael Ackermann <[email protected]> Reviewed-By: Rich Trott <[email protected]>
anchnk · May 19, 2017 · b7baf43 · b7baf43
1 parent 101b5ab
commit b7baf43
Showing 1 changed file with 15 additions and 6 deletions.
diff --git a/lib/assert.js b/lib/assert.js
@@ -285,15 +285,24 @@ function _deepEqual(actual, expected, strict, memos) {
   // Note: this accounts for both named and indexed properties on Arrays.
 
   // Use memos to handle cycles.
-  memos = memos || { actual: [], expected: [] };
-  const actualIndex = memos.actual.indexOf(actual);
-  if (actualIndex !== -1) {
-    if (actualIndex === memos.expected.indexOf(expected)) {
+  if (!memos) {
+    memos = {
+      actual: { map: new Map(), position: 0 },
+      expected: { map: new Map(), position: 0 }
+    };
+  }
+
+  const actualPosition = memos.actual.map.get(actual);
+  if (actualPosition !== undefined) {
+    if (actualPosition === memos.expected.map.get(expected)) {
       return true;
     }
+  } else {
+    memos.actual.map.set(actual, memos.actual.position++);
+  }
+  if (!memos.expected.map.has(expected)) {
+    memos.expected.map.set(expected, memos.expected.position++);
   }
-  memos.actual.push(actual);
-  memos.expected.push(expected);
 
   return objEquiv(actual, expected, strict, memos);
 }