Refuse the mark spellings that cannot open or close where they sit

src/json-value.ts

@@ -1,17 +1,22 @@
+import { largestNesting } from './nesting.ts'
+
 export type JsonValue = JsonValue[] | boolean | null | number | string | { [key: string]: JsonValue }
 
 export function isJsonValue(value: unknown): value is JsonValue {
-  const pending: unknown[] = [value]
+  const pending: { depth: number; item: unknown }[] = [{ depth: 0, item: value }]
   while (pending.length > 0) {
-    const item = pending.pop()
+    const entry = pending.pop()
+    if (entry === undefined) continue
+    const { depth, item } = entry
+    if (depth > largestNesting) return false
     if (item === null || typeof item === 'boolean' || typeof item === 'string') continue
     if (typeof item === 'number') {
       if (!Number.isFinite(item)) return false
       continue
     }
     // A hole is not a JSON value, and Array.prototype methods skip holes — spreading materialises them.
-    if (Array.isArray(item)) pending.push(...item)
-    else if (typeof item === 'object') pending.push(...Object.values(item))
+    if (Array.isArray(item)) for (const child of [...item]) pending.push({ depth: depth + 1, item: child })
+    else if (typeof item === 'object') for (const child of Object.values(item)) pending.push({ depth: depth + 1, item: child })
     else return false
   }
   return true