[Fix] stringify: actually fix cyclic references

Fixes #403.

Co-authored-by: liaokunhua <[email protected]>
Co-authored-by: Jordan Harband <[email protected]>

Author: liaokunhua

lib/stringify.js

@@ -56,6 +56,8 @@ var isNonNullishPrimitive = function isNonNullishPrimitive(v) {
         || typeof v === 'bigint';
 };
 
+var sentinel = {};
+
 var stringify = function stringify(
     object,
     prefix,
@@ -75,8 +77,23 @@ var stringify = function stringify(
 ) {
     var obj = object;
 
-    if (sideChannel.has(object)) {
-        throw new RangeError('Cyclic object value');
+    var tmpSc = sideChannel;
+    var step = 0;
+    var findFlag = false;
+    while ((tmpSc = tmpSc.get(sentinel)) !== undefined && !findFlag) {
+        // Where object last appeared in the ref tree
+        var pos = tmpSc.get(object);
+        step += 1;
+        if (typeof pos !== 'undefined') {
+            if (pos === step) {
+                throw new RangeError('Cyclic object value');
+            } else {
+                findFlag = true; // Break while
+            }
+        }
+        if (typeof tmpSc.get(sentinel) === 'undefined') {
+            step = 0;
+        }
     }
 
     if (typeof filter === 'function') {
@@ -145,8 +162,9 @@ var stringify = function stringify(
             ? typeof generateArrayPrefix === 'function' ? generateArrayPrefix(prefix, key) : prefix
             : prefix + (allowDots ? '.' + key : '[' + key + ']');
 
-        sideChannel.set(object, true);
+        sideChannel.set(object, step);
         var valueSideChannel = getSideChannel();
+        valueSideChannel.set(sentinel, sideChannel);
         pushToArray(values, stringify(
             value,
             keyPrefix,

test/stringify.js

@@ -454,7 +454,7 @@ test('stringify()', function (t) {
 
         st['throws'](
             function () { qs.stringify({ 'foo[bar]': 'baz', 'foo[baz]': a }); },
-            RangeError,
+            /RangeError: Cyclic object value/,
             'cyclic values throw'
         );
 
@@ -464,10 +464,16 @@ test('stringify()', function (t) {
         circular.a = circular;
         st['throws'](
             function () { qs.stringify(circular); },
-            RangeError,
+            /RangeError: Cyclic object value/,
             'cyclic values throw'
         );
 
+        var arr = ['a'];
+        st.doesNotThrow(
+            function () { qs.stringify({ x: arr, y: arr }); },
+            'non-cyclic values do not throw'
+        );
+
         st.end();
     });