util: use proper circular reference checking

Circular references are conceptually nothing that should be checked
for objects (or Sets or Maps) only, but applies to recursive structures
in general, so move the `seen` checks into a position where it is part
of the recursion itself.

Fixes: #1
PR-URL: #2

Author: withgit-contributor

lib/util.js

@@ -612,10 +612,13 @@ function formatValue(ctx, value, recurseTimes) {
     }
   }
 
-  ctx.seen.push(value);
-
-  var output = formatter(ctx, value, recurseTimes, visibleKeys, keys);
+  // TODO(addaleax): Make `seen` a Set to avoid linear-time lookup.
+  if (ctx.seen.includes(value)) {
+    return ctx.stylize('[Circular]', 'special');
+  }
 
+  ctx.seen.push(value);
+  const output = formatter(ctx, value, recurseTimes, visibleKeys, keys);
   ctx.seen.pop();
 
   return reduceToSingleString(output, base, braces, ctx.breakLength);
@@ -835,21 +838,17 @@ function formatProperty(ctx, value, recurseTimes, visibleKeys, key, array) {
     }
   }
   if (!str) {
-    if (ctx.seen.indexOf(desc.value) < 0) {
-      if (recurseTimes === null) {
-        str = formatValue(ctx, desc.value, null);
+    if (recurseTimes === null) {
+      str = formatValue(ctx, desc.value, null);
+    } else {
+      str = formatValue(ctx, desc.value, recurseTimes - 1);
+    }
+    if (str.indexOf('\n') > -1) {
+      if (array) {
+        str = str.replace(/\n/g, '\n  ');
       } else {
-        str = formatValue(ctx, desc.value, recurseTimes - 1);
-      }
-      if (str.indexOf('\n') > -1) {
-        if (array) {
-          str = str.replace(/\n/g, '\n  ');
-        } else {
-          str = str.replace(/^|\n/g, '\n   ');
-        }
+        str = str.replace(/^|\n/g, '\n   ');
       }
-    } else {
-      str = ctx.stylize('[Circular]', 'special');
     }
   }
   if (name === undefined) {