BigInt stringify order of steps

test/built-ins/JSON/stringify/bigint-order.js

@@ -0,0 +1,40 @@
+// Copyright (C) 2017 Robin Templeton. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: BigInt stringify order of steps
+esid: sec-serializejsonproperty
+info: >
+  Runtime Semantics: SerializeJSONProperty ( key, holder )
+
+  2. If Type(value) is Object or BigInt, then
+    a. Let toJSON be ? GetGetV(value, "toJSON").
+    b. If IsCallable(toJSON) is true, then
+      i. Set value to ? Call(toJSON, value, « key »).
+  3. If ReplacerFunction is not undefined, then
+    a. Set value to ? Call(ReplacerFunction, holder, « key, value »).
+  4. If Type(value) is Object, then
+    a. If value has a [[NumberData]] internal slot, then
+      i. Set value to ? ToNumber(value).
+  [...]
+  10. If Type(value) is BigInt, throw a TypeError exception
+features: [BigInt, arrow-function]
+---*/
+
+let step = 0;
+
+function replacer(k, v)
+{
+  assert.sameValue(step++, 1);
+  if (v === 1n) {
+    let x = Object(1);
+    x.valueOf = function () { assert.sameValue(step++, 2); return 2n; };
+    return x;
+  } else {
+    return v;
+  }
+}
+
+BigInt.prototype.toJSON = function () { assert.sameValue(step++, 0); return 1n; };
+assert.throws(TypeError, () => JSON.stringify(0n, replacer));
+assert.sameValue(step, 3);