feat(codemode): support JSON callbacks (#38006)

packages/codemode/interpreter-support.md

@@ -247,10 +247,15 @@ ultimate source of truth.
 
 - [x] `JSON.parse` and `JSON.stringify` for supported data objects; the blocked data-key gap listed above still applies.
 - [x] Numeric/string indentation for `JSON.stringify`.
+- [x] `JSON.parse` reviver callbacks, including postorder traversal, deletion through `undefined`, and root replacement.
+      Revivers receive `(key, value)` but no `this` holder because CodeMode functions intentionally have no `this`.
+- [x] `JSON.stringify` function and array replacers. Function replacers receive `(key, value)` in preorder, including
+      the root, but no `this` holder. Array replacers preserve requested property order, deduplicate names, coerce
+      number primitives, and ignore non-string/non-number entries. Primitive wrapper entries remain unsupported.
+- [x] JSON callbacks retain the blocked-key boundary: parsed or stringified data containing `__proto__`, `constructor`,
+      or `prototype` is rejected before callback traversal.
 - [x] Captured `console.log`, `console.info`, `console.debug`, `console.warn`, and `console.error`.
 - [x] Captured `console.dir` and `console.table`.
-- [ ] `JSON.parse` reviver callbacks.
-- [ ] `JSON.stringify` function/array replacers.
 
 ## Date
 

packages/codemode/src/interpreter/methods.ts

@@ -8,6 +8,7 @@ import {
   GlobalNamespace,
   IntrinsicReference,
   InterpreterRuntimeError,
+  JsonMethodReference,
   PromiseCapabilityFunction,
   PromiseNamespace,
   UriFunction,
@@ -25,7 +26,6 @@ import {
   isCodeModeValue,
 } from "../values.js"
 import { dateSetterArgumentCount, invokeDateMethod, invokeDateStatic } from "../stdlib/date.js"
-import { invokeJsonMethod } from "../stdlib/json.js"
 import { invokeMathMethod } from "../stdlib/math.js"
 import { invokeNumberMethod, invokeNumberStatic } from "../stdlib/number.js"
 import { invokeObjectMethod } from "../stdlib/object.js"
@@ -54,6 +54,7 @@ export type SupportedCallback =
   | UriFunction
   | PromiseCapabilityFunction
   | GlobalMethodReference
+  | JsonMethodReference
   | IntrinsicReference
   | ErrorConstructorReference
   | GlobalNamespace
@@ -65,6 +66,7 @@ export const isSupportedCallback = (value: unknown): value is SupportedCallback
   value instanceof UriFunction ||
   value instanceof PromiseCapabilityFunction ||
   value instanceof GlobalMethodReference ||
+  value instanceof JsonMethodReference ||
   value instanceof IntrinsicReference ||
   value instanceof ErrorConstructorReference ||
   // Callable namespaces dispatch like JS: Array/Object/Date/RegExp construct,
@@ -168,7 +170,7 @@ export const invokeGlobalMethod = (ref: GlobalMethodReference, args: Array<unkno
   if (ref.namespace === "Map" || ref.namespace === "Set" || ref.namespace === "URLSearchParams") {
     throw new InterpreterRuntimeError(`${ref.namespace}.${ref.name} is not available in CodeMode.`, node)
   }
-  return invokeJsonMethod(ref.name, args, node)
+  throw new InterpreterRuntimeError(`${ref.namespace}.${ref.name} is not available in CodeMode.`, node)
 }
 
 const requireDataArgument = (name: string, index: number, arg: unknown, node: AstNode): unknown => {

packages/codemode/src/interpreter/model.ts

@@ -99,11 +99,15 @@ export class GlobalNamespace {
 
 export class GlobalMethodReference {
   constructor(
-    readonly namespace: GlobalNamespaceName | "Number" | "String",
+    readonly namespace: Exclude<GlobalNamespaceName, "JSON"> | "Number" | "String",
     readonly name: string,
   ) {}
 }
 
+export class JsonMethodReference {
+  constructor(readonly name: "parse" | "stringify") {}
+}
+
 export class CoercionFunction {
   constructor(readonly name: "Number" | "String" | "Boolean" | "parseInt" | "parseFloat" | "isFinite" | "isNaN") {}
 }

packages/codemode/src/interpreter/references.ts

@@ -7,6 +7,7 @@ import {
   GlobalNamespace,
   InterpreterRuntimeError,
   IntrinsicReference,
+  JsonMethodReference,
   PromiseCapabilityFunction,
   PromiseInstanceMethodReference,
   PromiseMethodReference,
@@ -23,6 +24,7 @@ export const isRuntimeReference = (value: unknown): boolean =>
   value instanceof IntrinsicReference ||
   value instanceof GlobalNamespace ||
   value instanceof GlobalMethodReference ||
+  value instanceof JsonMethodReference ||
   value instanceof PromiseNamespace ||
   value instanceof PromiseMethodReference ||
   value instanceof PromiseInstanceMethodReference ||
@@ -82,12 +84,7 @@ export const containsOpaqueReference = (value: unknown): boolean => {
 }
 
 // Reject cycles before mutation so later boundary walks remain safe.
-export const rejectCircularInsertion = (
+export const rejectCircularInsertion = (container: object, value: unknown, label: string, node: AstNode): void => {
-  container: object,
-  value: unknown,
-  label: string,
-  node: AstNode,
-): void => {
   const pending: Array<Iterator<unknown>> = [[value].values()]
   const seen = new Set<object>()
   while (pending.length > 0) {
@@ -111,6 +108,7 @@ export const typeofValue = (value: unknown): string => {
     value instanceof CoercionFunction ||
     value instanceof IntrinsicReference ||
     value instanceof GlobalMethodReference ||
+    value instanceof JsonMethodReference ||
     value instanceof PromiseMethodReference ||
     value instanceof PromiseInstanceMethodReference ||
     value instanceof PromiseNamespace ||

packages/codemode/src/interpreter/runtime.ts

@@ -19,6 +19,7 @@ import {
   IntrinsicReference,
   InterpreterRuntimeError,
   isRecord,
+  JsonMethodReference,
   type MemberReference,
   OptionalShortCircuit,
   PromiseCapabilityFunction,
@@ -55,7 +56,7 @@ import { ScopeStack } from "./scope.js"
 import { arrayMethods, mapMethods, mapStatics, setMethods, spreadItems } from "../stdlib/collections.js"
 import { consoleMethods, formatConsoleMessage } from "../stdlib/console.js"
 import { dateMethods, dateStatics } from "../stdlib/date.js"
-import { jsonStatics } from "../stdlib/json.js"
+import { invokeJsonMethod, jsonStatics, type JsonMethodName } from "../stdlib/json.js"
 import { mathConstants, mathMethods } from "../stdlib/math.js"
 import { numberConstants, numberMethods, numberStatics } from "../stdlib/number.js"
 import { objectMethodsPreservingIdentity, objectStatics } from "../stdlib/object.js"
@@ -102,7 +103,6 @@ import {
 const globalStaticMembers: Partial<Record<GlobalNamespaceName, Set<string>>> = {
   Object: objectStatics,
   Math: mathMethods,
-  JSON: jsonStatics,
   Array: arrayStatics,
   console: consoleMethods,
   Date: dateStatics,
@@ -1624,6 +1624,9 @@ export class Interpreter<R> {
         }
         return boundedData(invokeGlobalMethod(callable, args, node), `${callable.namespace}.${callable.name} result`)
       }
+      if (callable instanceof JsonMethodReference) {
+        return yield* invokeJsonMethod(self.runner, callable.name, args, node)
+      }
       if (callable instanceof CoercionFunction) {
         return boundedData(invokeCoercion(callable, args, node), `${callable.name} result`)
       }
@@ -1889,6 +1892,7 @@ export class Interpreter<R> {
     | PromiseInstanceMethodReference
     | IntrinsicReference
     | GlobalMethodReference
+    | JsonMethodReference
     | ComputedValue
     | typeof OptionalShortCircuit
     | undefined,
@@ -1936,6 +1940,10 @@ export class Interpreter<R> {
         if (objectValue.name === "Math" && mathConstants.has(key)) {
           return new ComputedValue((Math as unknown as Record<string, number>)[key])
         }
+        if (objectValue.name === "JSON") {
+          if (jsonStatics.has(key)) return new JsonMethodReference(key as JsonMethodName)
+          return new ComputedValue(undefined)
+        }
         if (globalStaticMembers[objectValue.name]?.has(key)) {
           return new GlobalMethodReference(objectValue.name, key)
         }
@@ -2065,7 +2073,8 @@ export class Interpreter<R> {
         reference instanceof PromiseMethodReference ||
         reference instanceof PromiseInstanceMethodReference ||
         reference instanceof IntrinsicReference ||
-        reference instanceof GlobalMethodReference
+        reference instanceof GlobalMethodReference ||
+        reference instanceof JsonMethodReference
       )
         return reference
       if (Array.isArray(reference.target)) {
@@ -2100,6 +2109,7 @@ export class Interpreter<R> {
         reference instanceof PromiseInstanceMethodReference ||
         reference instanceof IntrinsicReference ||
         reference instanceof GlobalMethodReference ||
+        reference instanceof JsonMethodReference ||
         reference.target instanceof CodeModeURL
       ) {
         throw new InterpreterRuntimeError("Only data fields may be deleted in CodeMode.", target, "InvalidDataValue")
@@ -2127,7 +2137,8 @@ export class Interpreter<R> {
         reference instanceof PromiseMethodReference ||
         reference instanceof PromiseInstanceMethodReference ||
         reference instanceof IntrinsicReference ||
-        reference instanceof GlobalMethodReference
+        reference instanceof GlobalMethodReference ||
+        reference instanceof JsonMethodReference
       ) {
         throw new InterpreterRuntimeError("Only data fields may be assigned in CodeMode.", node)
       }

packages/codemode/src/stdlib/json.ts

@@ -1,45 +1,149 @@
-import { type AstNode, InterpreterRuntimeError, supportedSyntaxMessage } from "../interpreter/model.js"
+import { Effect } from "effect"
+import type { CallbackRunner } from "../interpreter/methods.js"
+import { applyCollectionCallback } from "../interpreter/methods.js"
+import { type AstNode, InterpreterRuntimeError } from "../interpreter/model.js"
 import { typeofValue } from "../interpreter/references.js"
-import { copyIn, copyOut } from "../tool-runtime.js"
+import { copyIn, copyOut, type SafeObject } from "../tool-runtime.js"
+import {
+  CodeModeDate,
+  CodeModeMap,
+  CodeModeRegExp,
+  CodeModeSet,
+  CodeModeURL,
+  CodeModeURLSearchParams,
+} from "../values.js"
 
 export const jsonStatics = new Set(["parse", "stringify"])
+export type JsonMethodName = "parse" | "stringify"
 
-export const invokeJsonMethod = (name: string, args: Array<unknown>, node: AstNode): unknown => {
+export const invokeJsonMethod = <R>(
-  switch (name) {
+  runner: CallbackRunner<R>,
-    case "stringify": {
+  name: JsonMethodName,
-      const replacer = args[1]
+  args: Array<unknown>,
-      if (Array.isArray(replacer) || typeofValue(replacer) === "function") {
+  node: AstNode,
-        throw new InterpreterRuntimeError(
+): Effect.Effect<unknown, unknown, R> => {
-          "JSON.stringify replacers are not supported in CodeMode.",
+  return name === "parse" ? parse(runner, args, node) : stringify(runner, args, node)
-          node,
-          "UnsupportedSyntax",
-          [supportedSyntaxMessage],
-        )
-      }
-      const space = args[2]
-      const indent = typeof space === "number" || typeof space === "string" ? space : undefined
-      return JSON.stringify(copyOut(copyIn(args[0], "JSON.stringify value"), "json"), null, indent)
-    }
-    case "parse": {
-      const text = args[0]
-      if (typeof text !== "string") throw new InterpreterRuntimeError("JSON.parse expects a string.", node)
-      if (typeofValue(args[1]) === "function") {
-        throw new InterpreterRuntimeError(
-          "JSON.parse revivers are not supported in CodeMode.",
-          node,
-          "UnsupportedSyntax",
-          [supportedSyntaxMessage],
-        )
-      }
-      try {
-        return copyIn(JSON.parse(text), "JSON.parse result")
-      } catch (error) {
-        throw new InterpreterRuntimeError(
-          `JSON.parse received invalid JSON: ${error instanceof Error ? error.message : String(error)}`,
-          node,
-        ).as("SyntaxError")
-      }
-    }
-  }
-  throw new InterpreterRuntimeError(`JSON.${name} is not available in CodeMode.`, node)
 }
+
+const parse = <R>(
+  runner: CallbackRunner<R>,
+  args: Array<unknown>,
+  node: AstNode,
+): Effect.Effect<unknown, unknown, R> => {
+  const text = args[0]
+  if (typeof text !== "string") throw new InterpreterRuntimeError("JSON.parse expects a string.", node)
+
+  const parsed = (() => {
+    try {
+      return copyIn(JSON.parse(text), "JSON.parse result")
+    } catch (error) {
+      throw new InterpreterRuntimeError(
+        `JSON.parse received invalid JSON: ${error instanceof Error ? error.message : String(error)}`,
+        node,
+      ).as("SyntaxError")
+    }
+  })()
+  if (typeofValue(args[1]) !== "function") return Effect.succeed(parsed)
+
+  const apply = applyCollectionCallback(runner, args[1], "JSON.parse", node)
+  const root: SafeObject = Object.create(null) as SafeObject
+  root[""] = parsed
+  const visit = (holder: SafeObject | Array<unknown>, key: string): Effect.Effect<unknown, unknown, R> =>
+    Effect.gen(function* () {
+      const value = holder[key as keyof typeof holder]
+      if (Array.isArray(value)) {
+        const length = value.length
+        for (let index = 0; index < length; index += 1) {
+          const revived = yield* visit(value, String(index))
+          if (revived === undefined) Reflect.deleteProperty(value, index)
+          else value[index] = revived
+        }
+      } else if (isPlainObject(value)) {
+        for (const name of Object.keys(value)) {
+          const revived = yield* visit(value, name)
+          if (revived === undefined) Reflect.deleteProperty(value, name)
+          else value[name] = revived
+        }
+      }
+      return yield* apply([key, value])
+    })
+  return visit(root, "")
+}
+
+const stringify = <R>(
+  runner: CallbackRunner<R>,
+  args: Array<unknown>,
+  node: AstNode,
+): Effect.Effect<unknown, unknown, R> => {
+  const space = args[2]
+  const indent = typeof space === "number" || typeof space === "string" ? space : undefined
+  const replacer = args[1]
+  const callable = typeofValue(replacer) === "function"
+  const checked = copyIn(args[0], "JSON.stringify value", callable)
+  const input = callable ? args[0] : checked
+
+  if (Array.isArray(replacer)) {
+    const properties = replacer
+      .filter((item): item is string | number => typeof item === "string" || typeof item === "number")
+      .map(String)
+    return Effect.succeed(JSON.stringify(copyOut(input, "json"), properties, indent))
+  }
+  if (!callable) {
+    return Effect.succeed(JSON.stringify(copyOut(input, "json"), null, indent))
+  }
+
+  const apply = applyCollectionCallback(runner, replacer, "JSON.stringify", node)
+  const root: SafeObject = Object.create(null) as SafeObject
+  root[""] = input
+  const stack = new Set<object>()
+  const visit = (holder: SafeObject | Array<unknown>, key: string): Effect.Effect<unknown, unknown, R> =>
+    Effect.gen(function* () {
+      const value = yield* apply([key, toJSONValue(holder[key as keyof typeof holder])])
+      if (value === undefined || typeofValue(value) === "function") return undefined
+      copyIn(value, "JSON.stringify replacer result", true)
+      if (typeof value === "number") return Number.isFinite(value) ? value : null
+      if (value === null || typeof value === "string" || typeof value === "boolean") return value
+      if (Array.isArray(value)) {
+        if (stack.has(value))
+          throw new InterpreterRuntimeError("Converting circular structure to JSON.", node).as("TypeError")
+        stack.add(value)
+        const result: Array<unknown> = []
+        for (let index = 0; index < value.length; index += 1) {
+          result.push((yield* visit(value, String(index))) ?? null)
+        }
+        stack.delete(value)
+        return result
+      }
+      if (!isPlainObject(value)) return {}
+      if (stack.has(value))
+        throw new InterpreterRuntimeError("Converting circular structure to JSON.", node).as("TypeError")
+      stack.add(value)
+      const result: SafeObject = Object.create(null) as SafeObject
+      for (const name of Object.keys(value)) {
+        const item = yield* visit(value, name)
+        if (item !== undefined) result[name] = item
+      }
+      stack.delete(value)
+      return result
+    })
+
+  return Effect.map(visit(root, ""), (value) => JSON.stringify(value, null, indent))
+}
+
+const toJSONValue = (value: unknown): unknown => {
+  if (value instanceof CodeModeDate) {
+    return Number.isFinite(value.time) ? new Date(value.time).toISOString() : null
+  }
+  if (value instanceof CodeModeURL) return value.url.href
+  return value
+}
+
+const isPlainObject = (value: unknown): value is SafeObject =>
+  value !== null &&
+  typeof value === "object" &&
+  !(value instanceof CodeModeDate) &&
+  !(value instanceof CodeModeRegExp) &&
+  !(value instanceof CodeModeMap) &&
+  !(value instanceof CodeModeSet) &&
+  !(value instanceof CodeModeURL) &&
+  !(value instanceof CodeModeURLSearchParams)

packages/codemode/test/callbacks.test.ts

@@ -285,21 +285,21 @@ describe("still-rejected callables get the wrap hint", () => {
     expect(diagnostic.message).toContain("wrap it in an arrow function")
   })
 
-  test("callable JSON.stringify replacers are rejected, never silently ignored", async () => {
+  test("JSON callbacks use the unified callback gate", async () => {
-    expect((await error(`return JSON.stringify({ a: 1 }, Math.abs)`)).message).toContain(
+    expect(
-      "JSON.stringify replacers are not supported",
+      await value(`return JSON.stringify({ a: -1 }, (key, item) => typeof item === "number" ? Math.abs(item) : item)`),
-    )
+    ).toBe('{"a":1}')
     expect((await toolError(`return JSON.stringify({ a: 1 }, tools.host.echo)`)).message).toContain(
-      "JSON.stringify replacers are not supported",
+      "wrap it in an arrow function",
+    )
+    expect((await toolError(`return JSON.parse('{"a":1}', tools.host.echo)`)).message).toContain(
+      "wrap it in an arrow function",
     )
   })
 
-  test("callable JSON.parse revivers are rejected, never silently ignored", async () => {
+  test("non-callable JSON callback arguments are ignored", async () => {
-    expect((await error(`return JSON.parse('{"a":1}', (key, v) => 99)`)).message).toContain(
-      "JSON.parse revivers are not supported",
-    )
     expect(await value(`return JSON.parse('{"a":1}', undefined)`)).toEqual({ a: 1 })
-    // A non-callable reviver is silently ignored, matching JS's IsCallable check.
     expect(await value(`return JSON.parse('{"a":1}', 42)`)).toEqual({ a: 1 })
+    expect(await value(`return JSON.stringify({ a: 1 }, 42)`)).toBe('{"a":1}')
   })
 })

packages/codemode/test/json-callbacks-test262.test.ts

@@ -0,0 +1,243 @@
+/*
+ * Portions adapted from Test262 at revision 250f204f23a9249ff204be2baec29600faae7b75:
+ * - test/built-ins/JSON/parse/reviver-call-order.js
+ * - test/built-ins/JSON/parse/reviver-call-err.js
+ * - test/built-ins/JSON/stringify/replacer-array-duplicates.js
+ * - test/built-ins/JSON/stringify/replacer-array-empty.js
+ * - test/built-ins/JSON/stringify/replacer-array-number.js
+ * - test/built-ins/JSON/stringify/replacer-array-order.js
+ * - test/built-ins/JSON/stringify/replacer-array-undefined.js
+ * - test/built-ins/JSON/stringify/replacer-array-wrong-type.js
+ * - test/built-ins/JSON/stringify/replacer-function-abrupt.js
+ * - test/built-ins/JSON/stringify/replacer-function-arguments.js
+ * - test/built-ins/JSON/stringify/replacer-function-array-circular.js
+ * - test/built-ins/JSON/stringify/replacer-function-object-deleted-property.js
+ * - test/built-ins/JSON/stringify/replacer-function-object-circular.js
+ * - test/built-ins/JSON/stringify/replacer-function-result-undefined.js
+ * - test/built-ins/JSON/stringify/replacer-function-result.js
+ *
+ * Function-context assertions are omitted because CodeMode functions intentionally
+ * have no `this`. Number/String wrapper cases are omitted because CodeMode does not
+ * support primitive wrapper objects. Proxy and Symbol cases are outside CodeMode.
+ *
+ * Copyright (C) 2012 Ecma International. All rights reserved.
+ * Copyright (C) 2016 the V8 project authors. All rights reserved.
+ * Copyright (C) 2019 Aleksey Shvayka. All rights reserved.
+ * Copyright 2019 Kevin Gibbons. All rights reserved.
+ * Test262 portions are governed by the BSD license in LICENSE.test262.
+ */
+import { describe, expect, test } from "bun:test"
+import { Effect } from "effect"
+import { CodeMode } from "../src/index.js"
+import { invokeJsonMethod } from "../src/stdlib/json.js"
+
+const value = async (code: string) => {
+  const result = await Effect.runPromise(CodeMode.execute({ code, tools: {} }))
+  if (!result.ok) throw new Error(`expected success, got ${result.error.kind}: ${result.error.message}`)
+  return result.value
+}
+
+describe("Test262 JSON.parse reviver adaptations", () => {
+  test("test/built-ins/JSON/parse/reviver-call-order.js", async () => {
+    expect(
+      await value(`
+        const calls = []
+        JSON.parse('{"p1":0,"p2":0,"p1":0,"2":0,"1":0}', (key, item) => {
+          calls.push(key)
+          return item
+        })
+        return calls
+      `),
+    ).toEqual(["1", "2", "p1", "p2", ""])
+  })
+
+  test("deletes properties and array elements when the reviver returns undefined", async () => {
+    expect(
+      await value(`
+        const result = JSON.parse('{"keep":1,"drop":2,"items":[1,2,3]}', (key, item) => {
+          if (key === "drop" || key === "1") return undefined
+          return item
+        })
+        return [result, Object.hasOwn(result, "drop"), Object.hasOwn(result.items, 1), result.items.length]
+      `),
+    ).toEqual([{ keep: 1, items: [1, null, 3] }, false, false, 3])
+  })
+
+  test("replaces the root and may delete it", async () => {
+    expect(await value(`return JSON.parse('{"a":1}', (key, item) => key === "" ? item.a : item)`)).toBe(1)
+    expect(
+      await value(`return JSON.parse('{"a":1}', (key, item) => key === "" ? undefined : item) === undefined`),
+    ).toBe(true)
+  })
+
+  test("test/built-ins/JSON/parse/reviver-call-err.js", async () => {
+    expect(
+      await value(`try { JSON.parse("0", () => { throw "stop" }) } catch (error) { return error } return "missed"`),
+    ).toBe("stop")
+  })
+})
+
+describe("Test262 JSON.stringify replacer adaptations", () => {
+  test("array replacers filter keys in their own order and apply recursively", async () => {
+    expect(await value(`return JSON.stringify({ b: 1, a: 2, c: 3 }, ["c", "b", "a"])`)).toBe('{"c":3,"b":1,"a":2}')
+    expect(await value(`return JSON.stringify({ a: { b: 2, c: 3 } }, ["c", "b", "a"])`)).toBe('{"a":{"c":3,"b":2}}')
+    expect(await value(`return JSON.stringify({ a: 1 }, [])`)).toBe("{}")
+  })
+
+  test("array replacers deduplicate and coerce number primitives", async () => {
+    expect(await value(`return JSON.stringify({ a: 1, b: 2 }, ["a", "a", "b"])`)).toBe('{"a":1,"b":2}')
+    expect(
+      await value(
+        `return JSON.stringify({ "0": 0, "1": 1, "-4": 2, "0.3": 3, "-Infinity": 4, "NaN": 5 }, [-0, 1, -4, 0.3, -Infinity, NaN])`,
+      ),
+    ).toBe('{"0":0,"1":1,"-4":2,"0.3":3,"-Infinity":4,"NaN":5}')
+  })
+
+  test("array replacers ignore unsupported entry types", async () => {
+    expect(
+      await value(`return JSON.stringify({ true: 1, false: 2, null: 3, kept: 4 }, [true, false, null, {}, "kept"])`),
+    ).toBe('{"kept":4}')
+    expect(await value(`return JSON.stringify({ a: 1 }, undefined)`)).toBe('{"a":1}')
+  })
+
+  test("function replacers receive keys and values in preorder including the root", async () => {
+    expect(
+      await value(`
+        const calls = []
+        const output = JSON.stringify({ a: [1, 2], b: true }, (key, item) => {
+          calls.push([key, Array.isArray(item) ? "array" : typeof item])
+          return item
+        })
+        return [output, calls]
+      `),
+    ).toEqual([
+      '{"a":[1,2],"b":true}',
+      [
+        ["", "object"],
+        ["a", "array"],
+        ["0", "number"],
+        ["1", "number"],
+        ["b", "boolean"],
+      ],
+    ])
+  })
+
+  test("test/built-ins/JSON/stringify/replacer-function-object-deleted-property.js", async () => {
+    expect(
+      await value(`
+        const input = { a: 1, b: 2 }
+        return JSON.stringify(input, (key, item) => {
+          if (key === "a") delete input.b
+          if (key === "b" && item === undefined) return "<replaced>"
+          return item
+        })
+      `),
+    ).toBe('{"a":1,"b":"<replaced>"}')
+  })
+
+  test("test/built-ins/JSON/stringify/replacer-function-object-circular.js", async () => {
+    expect(
+      await value(`
+        const direct = { prop: {} }
+        const indirect = { p1: { p2: {} } }
+        const errors = []
+        try { JSON.stringify(direct, () => direct) } catch (error) { errors.push(error.name) }
+        try {
+          JSON.stringify(indirect, (key, item) => key === "p2" ? indirect : item)
+        } catch (error) { errors.push(error.name) }
+        return errors
+      `),
+    ).toEqual(["TypeError", "TypeError"])
+  })
+
+  test("test/built-ins/JSON/stringify/replacer-function-array-circular.js", async () => {
+    expect(
+      await value(`
+        const circular = [{}]
+        try { JSON.stringify(circular, () => circular) } catch (error) { return error.name }
+        return "missed"
+      `),
+    ).toBe("TypeError")
+  })
+
+  test("repeated objects outside the active ancestor chain are not circular", async () => {
+    expect(
+      await value(`
+        const shared = { value: 1 }
+        return JSON.stringify({ left: shared, right: shared }, (key, item) => item)
+      `),
+    ).toBe('{"left":{"value":1},"right":{"value":1}}')
+  })
+
+  test("function replacers replace values and map undefined to omission or null", async () => {
+    expect(
+      await value(`return JSON.stringify({ a: 1, nested: { b: [1] } }, (key, item) => item === 1 ? undefined : item)`),
+    ).toBe('{"nested":{"b":[null]}}')
+    expect(await value(`return JSON.stringify(null, (key) => key === "" ? { value: 1 } : 2)`)).toBe('{"value":2}')
+    expect(await value(`return JSON.stringify(1, () => undefined) === undefined`)).toBe(true)
+  })
+
+  test("callable replacer results follow JSON omission semantics", async () => {
+    expect(
+      await value(`
+        const fn = () => 1
+        return [
+          JSON.stringify({ user: 1, builtin: 2 }, (key, item) => key === "user" ? fn : key === "builtin" ? Math.abs : item),
+          JSON.stringify([1, 2], (key, item) => key === "0" ? fn : key === "1" ? Number : item),
+          JSON.stringify(null, () => "abc".includes) === undefined,
+        ]
+      `),
+    ).toEqual(["{}", "[null,null]", true])
+  })
+
+  test("built-in toJSON conversion runs before the function replacer", async () => {
+    expect(
+      await value(`
+        const seen = []
+        const output = JSON.stringify({ date: new Date(0), url: new URL("https://example.test/a") }, (key, item) => {
+          if (key === "date" || key === "url") seen.push(typeof item)
+          return item
+        })
+        return [output, seen]
+      `),
+    ).toEqual(['{"date":"1970-01-01T00:00:00.000Z","url":"https://example.test/a"}', ["string", "string"]])
+  })
+
+  test("test/built-ins/JSON/stringify/replacer-function-abrupt.js", async () => {
+    expect(
+      await value(`try { JSON.stringify({}, () => { throw "stop" }) } catch (error) { return error } return "missed"`),
+    ).toBe("stop")
+  })
+})
+
+describe("CodeMode JSON callback boundaries", () => {
+  test("this remains unsupported rather than exposing callback holders", async () => {
+    const result = await Effect.runPromise(
+      CodeMode.execute({ code: `return JSON.parse("1", function (key, item) { return this })`, tools: {} }),
+    )
+    expect(result).toMatchObject({ ok: false, error: { kind: "UnsupportedSyntax" } })
+  })
+
+  test("blocked parse keys are rejected before reviver traversal", async () => {
+    expect(
+      await value(
+        `try { JSON.parse('{"__proto__":1}', (key, item) => item) } catch (error) { return true } return false`,
+      ),
+    ).toBe(true)
+  })
+
+  test("JSON.stringify directly rejects blocked input keys", () => {
+    expect(() =>
+      invokeJsonMethod(
+        {
+          invokeFunction: () => Effect.die("unused"),
+          invokeCallable: () => Effect.die("unused"),
+          settlePromise: () => Effect.die("unused"),
+        },
+        "stringify",
+        [Object.fromEntries([["constructor", 1]])],
+        { type: "CallExpression" },
+      ),
+    ).toThrow("blocked property 'constructor'")
+  })
+})

packages/codemode/test/parity.test.ts

@@ -889,6 +889,9 @@ describe("coercion parity: unknown static members read as undefined", () => {
       "TypeError: Math.sum is not a function.",
     )
     expect(await value(`try { Math["sum"]([1]) } catch (e) { return e.message }`)).toBe("Math.sum is not a function.")
+    expect(await value(`try { JSON.rawJSON("1") } catch (e) { return e.message }`)).toBe(
+      "JSON.rawJSON is not a function.",
+    )
   })
 
   test("blocked members still throw instead of reading as undefined", async () => {