diff -r 000000000000 -r 6474c204b198 js/src/json.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/json.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,892 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "json.h"
+
+#include "mozilla/FloatingPoint.h"
+
+#include "jsarray.h"
+#include "jsatom.h"
+#include "jscntxt.h"
+#include "jsnum.h"
+#include "jsobj.h"
+#include "jsonparser.h"
+#include "jsstr.h"
+#include "jstypes.h"
+#include "jsutil.h"
+
+#include "vm/Interpreter.h"
+#include "vm/StringBuffer.h"
+
+#include "jsatominlines.h"
+#include "jsboolinlines.h"
+#include "jsobjinlines.h"
+
+using namespace js;
+using namespace js::gc;
+using namespace js::types;
+
+using mozilla::IsFinite;
+using mozilla::Maybe;
+
+const Class js::JSONClass = {
+    js_JSON_str,
+    JSCLASS_HAS_CACHED_PROTO(JSProto_JSON),
+    JS_PropertyStub,        /* addProperty */
+    JS_DeletePropertyStub,  /* delProperty */
+    JS_PropertyStub,        /* getProperty */
+    JS_StrictPropertyStub,  /* setProperty */
+    JS_EnumerateStub,
+    JS_ResolveStub,
+    JS_ConvertStub
+};
+
+static inline bool IsQuoteSpecialCharacter(jschar c)
+{
+    JS_STATIC_ASSERT('\b' < ' ');
+    JS_STATIC_ASSERT('\f' < ' ');
+    JS_STATIC_ASSERT('\n' < ' ');
+    JS_STATIC_ASSERT('\r' < ' ');
+    JS_STATIC_ASSERT('\t' < ' ');
+    return c == '"' || c == '\\' || c < ' ';
+}
+
+/* ES5 15.12.3 Quote. */
+static bool
+Quote(JSContext *cx, StringBuffer &sb, JSString *str)
+{
+    JS::Anchor<JSString *> anchor(str);
+    size_t len = str->length();
+    const jschar *buf = str->getChars(cx);
+    if (!buf)
+        return false;
+
+    /* Step 1. */
+    if (!sb.append('"'))
+        return false;
+
+    /* Step 2. */
+    for (size_t i = 0; i < len; ++i) {
+        /* Batch-append maximal character sequences containing no escapes. */
+        size_t mark = i;
+        do {
+            if (IsQuoteSpecialCharacter(buf[i]))
+                break;
+        } while (++i < len);
+        if (i > mark) {
+            if (!sb.append(&buf[mark], i - mark))
+                return false;
+            if (i == len)
+                break;
+        }
+
+        jschar c = buf[i];
+        if (c == '"' || c == '\\') {
+            if (!sb.append('\\') || !sb.append(c))
+                return false;
+        } else if (c == '\b' || c == '\f' || c == '\n' || c == '\r' || c == '\t') {
+           jschar abbrev = (c == '\b')
+                         ? 'b'
+                         : (c == '\f')
+                         ? 'f'
+                         : (c == '\n')
+                         ? 'n'
+                         : (c == '\r')
+                         ? 'r'
+                         : 't';
+           if (!sb.append('\\') || !sb.append(abbrev))
+               return false;
+        } else {
+            JS_ASSERT(c < ' ');
+            if (!sb.append("\\u00"))
+                return false;
+            JS_ASSERT((c >> 4) < 10);
+            uint8_t x = c >> 4, y = c % 16;
+            if (!sb.append('0' + x) || !sb.append(y < 10 ? '0' + y : 'a' + (y - 10)))
+                return false;
+        }
+    }
+
+    /* Steps 3-4. */
+    return sb.append('"');
+}
+
+namespace {
+
+class StringifyContext
+{
+  public:
+    StringifyContext(JSContext *cx, StringBuffer &sb, const StringBuffer &gap,
+                     HandleObject replacer, const AutoIdVector &propertyList)
+      : sb(sb),
+        gap(gap),
+        replacer(cx, replacer),
+        propertyList(propertyList),
+        depth(0)
+    {}
+
+    StringBuffer &sb;
+    const StringBuffer &gap;
+    RootedObject replacer;
+    const AutoIdVector &propertyList;
+    uint32_t depth;
+};
+
+} /* anonymous namespace */
+
+static bool Str(JSContext *cx, const Value &v, StringifyContext *scx);
+
+static bool
+WriteIndent(JSContext *cx, StringifyContext *scx, uint32_t limit)
+{
+    if (!scx->gap.empty()) {
+        if (!scx->sb.append('\n'))
+            return false;
+        for (uint32_t i = 0; i < limit; i++) {
+            if (!scx->sb.append(scx->gap.begin(), scx->gap.end()))
+                return false;
+        }
+    }
+
+    return true;
+}
+
+namespace {
+
+template<typename KeyType>
+class KeyStringifier {
+};
+
+template<>
+class KeyStringifier<uint32_t> {
+  public:
+    static JSString *toString(JSContext *cx, uint32_t index) {
+        return IndexToString(cx, index);
+    }
+};
+
+template<>
+class KeyStringifier<HandleId> {
+  public:
+    static JSString *toString(JSContext *cx, HandleId id) {
+        return IdToString(cx, id);
+    }
+};
+
+} /* anonymous namespace */
+
+/*
+ * ES5 15.12.3 Str, steps 2-4, extracted to enable preprocessing of property
+ * values when stringifying objects in JO.
+ */
+template<typename KeyType>
+static bool
+PreprocessValue(JSContext *cx, HandleObject holder, KeyType key, MutableHandleValue vp, StringifyContext *scx)
+{
+    RootedString keyStr(cx);
+
+    /* Step 2. */
+    if (vp.isObject()) {
+        RootedValue toJSON(cx);
+        RootedObject obj(cx, &vp.toObject());
+        if (!JSObject::getProperty(cx, obj, obj, cx->names().toJSON, &toJSON))
+            return false;
+
+        if (js_IsCallable(toJSON)) {
+            keyStr = KeyStringifier<KeyType>::toString(cx, key);
+            if (!keyStr)
+                return false;
+
+            InvokeArgs args(cx);
+            if (!args.init(1))
+                return false;
+
+            args.setCallee(toJSON);
+            args.setThis(vp);
+            args[0].setString(keyStr);
+
+            if (!Invoke(cx, args))
+                return false;
+            vp.set(args.rval());
+        }
+    }
+
+    /* Step 3. */
+    if (scx->replacer && scx->replacer->isCallable()) {
+        if (!keyStr) {
+            keyStr = KeyStringifier<KeyType>::toString(cx, key);
+            if (!keyStr)
+                return false;
+        }
+
+        InvokeArgs args(cx);
+        if (!args.init(2))
+            return false;
+
+        args.setCallee(ObjectValue(*scx->replacer));
+        args.setThis(ObjectValue(*holder));
+        args[0].setString(keyStr);
+        args[1].set(vp);
+
+        if (!Invoke(cx, args))
+            return false;
+        vp.set(args.rval());
+    }
+
+    /* Step 4. */
+    if (vp.get().isObject()) {
+        RootedObject obj(cx, &vp.get().toObject());
+        if (ObjectClassIs(obj, ESClass_Number, cx)) {
+            double d;
+            if (!ToNumber(cx, vp, &d))
+                return false;
+            vp.set(NumberValue(d));
+        } else if (ObjectClassIs(obj, ESClass_String, cx)) {
+            JSString *str = ToStringSlow<CanGC>(cx, vp);
+            if (!str)
+                return false;
+            vp.set(StringValue(str));
+        } else if (ObjectClassIs(obj, ESClass_Boolean, cx)) {
+            vp.setBoolean(BooleanGetPrimitiveValue(obj));
+        }
+    }
+
+    return true;
+}
+
+/*
+ * Determines whether a value which has passed by ES5 150.2.3 Str steps 1-4's
+ * gauntlet will result in Str returning |undefined|.  This function is used to
+ * properly omit properties resulting in such values when stringifying objects,
+ * while properly stringifying such properties as null when they're encountered
+ * in arrays.
+ */
+static inline bool
+IsFilteredValue(const Value &v)
+{
+    return v.isUndefined() || js_IsCallable(v);
+}
+
+/* ES5 15.12.3 JO. */
+static bool
+JO(JSContext *cx, HandleObject obj, StringifyContext *scx)
+{
+    /*
+     * This method implements the JO algorithm in ES5 15.12.3, but:
+     *
+     *   * The algorithm is somewhat reformulated to allow the final string to
+     *     be streamed into a single buffer, rather than be created and copied
+     *     into place incrementally as the ES5 algorithm specifies it.  This
+     *     requires moving portions of the Str call in 8a into this algorithm
+     *     (and in JA as well).
+     */
+
+    /* Steps 1-2, 11. */
+    AutoCycleDetector detect(cx, obj);
+    if (!detect.init())
+        return false;
+    if (detect.foundCycle()) {
+        JS_ReportErrorNumber(cx, js_GetErrorMessage, nullptr, JSMSG_CYCLIC_VALUE, js_object_str);
+        return false;
+    }
+
+    if (!scx->sb.append('{'))
+        return false;
+
+    /* Steps 5-7. */
+    Maybe<AutoIdVector> ids;
+    const AutoIdVector *props;
+    if (scx->replacer && !scx->replacer->isCallable()) {
+        JS_ASSERT(JS_IsArrayObject(cx, scx->replacer));
+        props = &scx->propertyList;
+    } else {
+        JS_ASSERT_IF(scx->replacer, scx->propertyList.length() == 0);
+        ids.construct(cx);
+        if (!GetPropertyNames(cx, obj, JSITER_OWNONLY, ids.addr()))
+            return false;
+        props = ids.addr();
+    }
+
+    /* My kingdom for not-quite-initialized-from-the-start references. */
+    const AutoIdVector &propertyList = *props;
+
+    /* Steps 8-10, 13. */
+    bool wroteMember = false;
+    RootedId id(cx);
+    for (size_t i = 0, len = propertyList.length(); i < len; i++) {
+        /*
+         * Steps 8a-8b.  Note that the call to Str is broken up into 1) getting
+         * the property; 2) processing for toJSON, calling the replacer, and
+         * handling boxed Number/String/Boolean objects; 3) filtering out
+         * values which process to |undefined|, and 4) stringifying all values
+         * which pass the filter.
+         */
+        id = propertyList[i];
+        RootedValue outputValue(cx);
+        if (!JSObject::getGeneric(cx, obj, obj, id, &outputValue))
+            return false;
+        if (!PreprocessValue(cx, obj, HandleId(id), &outputValue, scx))
+            return false;
+        if (IsFilteredValue(outputValue))
+            continue;
+
+        /* Output a comma unless this is the first member to write. */
+        if (wroteMember && !scx->sb.append(','))
+            return false;
+        wroteMember = true;
+
+        if (!WriteIndent(cx, scx, scx->depth))
+            return false;
+
+        JSString *s = IdToString(cx, id);
+        if (!s)
+            return false;
+
+        if (!Quote(cx, scx->sb, s) ||
+            !scx->sb.append(':') ||
+            !(scx->gap.empty() || scx->sb.append(' ')) ||
+            !Str(cx, outputValue, scx))
+        {
+            return false;
+        }
+    }
+
+    if (wroteMember && !WriteIndent(cx, scx, scx->depth - 1))
+        return false;
+
+    return scx->sb.append('}');
+}
+
+/* ES5 15.12.3 JA. */
+static bool
+JA(JSContext *cx, HandleObject obj, StringifyContext *scx)
+{
+    /*
+     * This method implements the JA algorithm in ES5 15.12.3, but:
+     *
+     *   * The algorithm is somewhat reformulated to allow the final string to
+     *     be streamed into a single buffer, rather than be created and copied
+     *     into place incrementally as the ES5 algorithm specifies it.  This
+     *     requires moving portions of the Str call in 8a into this algorithm
+     *     (and in JO as well).
+     */
+
+    /* Steps 1-2, 11. */
+    AutoCycleDetector detect(cx, obj);
+    if (!detect.init())
+        return false;
+    if (detect.foundCycle()) {
+        JS_ReportErrorNumber(cx, js_GetErrorMessage, nullptr, JSMSG_CYCLIC_VALUE, js_object_str);
+        return false;
+    }
+
+    if (!scx->sb.append('['))
+        return false;
+
+    /* Step 6. */
+    uint32_t length;
+    if (!GetLengthProperty(cx, obj, &length))
+        return false;
+
+    /* Steps 7-10. */
+    if (length != 0) {
+        /* Steps 4, 10b(i). */
+        if (!WriteIndent(cx, scx, scx->depth))
+            return false;
+
+        /* Steps 7-10. */
+        RootedValue outputValue(cx);
+        for (uint32_t i = 0; i < length; i++) {
+            /*
+             * Steps 8a-8c.  Again note how the call to the spec's Str method
+             * is broken up into getting the property, running it past toJSON
+             * and the replacer and maybe unboxing, and interpreting some
+             * values as |null| in separate steps.
+             */
+            if (!JSObject::getElement(cx, obj, obj, i, &outputValue))
+                return false;
+            if (!PreprocessValue(cx, obj, i, &outputValue, scx))
+                return false;
+            if (IsFilteredValue(outputValue)) {
+                if (!scx->sb.append("null"))
+                    return false;
+            } else {
+                if (!Str(cx, outputValue, scx))
+                    return false;
+            }
+
+            /* Steps 3, 4, 10b(i). */
+            if (i < length - 1) {
+                if (!scx->sb.append(','))
+                    return false;
+                if (!WriteIndent(cx, scx, scx->depth))
+                    return false;
+            }
+        }
+
+        /* Step 10(b)(iii). */
+        if (!WriteIndent(cx, scx, scx->depth - 1))
+            return false;
+    }
+
+    return scx->sb.append(']');
+}
+
+static bool
+Str(JSContext *cx, const Value &v, StringifyContext *scx)
+{
+    /* Step 11 must be handled by the caller. */
+    JS_ASSERT(!IsFilteredValue(v));
+
+    JS_CHECK_RECURSION(cx, return false);
+
+    /*
+     * This method implements the Str algorithm in ES5 15.12.3, but:
+     *
+     *   * We move property retrieval (step 1) into callers to stream the
+     *     stringification process and avoid constantly copying strings.
+     *   * We move the preprocessing in steps 2-4 into a helper function to
+     *     allow both JO and JA to use this method.  While JA could use it
+     *     without this move, JO must omit any |undefined|-valued property per
+     *     so it can't stream out a value using the Str method exactly as
+     *     defined by ES5.
+     *   * We move step 11 into callers, again to ease streaming.
+     */
+
+    /* Step 8. */
+    if (v.isString())
+        return Quote(cx, scx->sb, v.toString());
+
+    /* Step 5. */
+    if (v.isNull())
+        return scx->sb.append("null");
+
+    /* Steps 6-7. */
+    if (v.isBoolean())
+        return v.toBoolean() ? scx->sb.append("true") : scx->sb.append("false");
+
+    /* Step 9. */
+    if (v.isNumber()) {
+        if (v.isDouble()) {
+            if (!IsFinite(v.toDouble()))
+                return scx->sb.append("null");
+        }
+
+        StringBuffer sb(cx);
+        if (!NumberValueToStringBuffer(cx, v, sb))
+            return false;
+
+        return scx->sb.append(sb.begin(), sb.length());
+    }
+
+    /* Step 10. */
+    JS_ASSERT(v.isObject());
+    RootedObject obj(cx, &v.toObject());
+
+    scx->depth++;
+    bool ok;
+    if (ObjectClassIs(obj, ESClass_Array, cx))
+        ok = JA(cx, obj, scx);
+    else
+        ok = JO(cx, obj, scx);
+    scx->depth--;
+
+    return ok;
+}
+
+/* ES5 15.12.3. */
+bool
+js_Stringify(JSContext *cx, MutableHandleValue vp, JSObject *replacer_, Value space_,
+             StringBuffer &sb)
+{
+    RootedObject replacer(cx, replacer_);
+    RootedValue space(cx, space_);
+
+    /* Step 4. */
+    AutoIdVector propertyList(cx);
+    if (replacer) {
+        if (replacer->isCallable()) {
+            /* Step 4a(i): use replacer to transform values.  */
+        } else if (ObjectClassIs(replacer, ESClass_Array, cx)) {
+            /*
+             * Step 4b: The spec algorithm is unhelpfully vague about the exact
+             * steps taken when the replacer is an array, regarding the exact
+             * sequence of [[Get]] calls for the array's elements, when its
+             * overall length is calculated, whether own or own plus inherited
+             * properties are considered, and so on.  A rewrite was proposed in
+             * <https://mail.mozilla.org/pipermail/es5-discuss/2011-April/003976.html>,
+             * whose steps are copied below, and which are implemented here.
+             *
+             * i.   Let PropertyList be an empty internal List.
+             * ii.  Let len be the result of calling the [[Get]] internal
+             *      method of replacer with the argument "length".
+             * iii. Let i be 0.
+             * iv.  While i < len:
+             *      1. Let item be undefined.
+             *      2. Let v be the result of calling the [[Get]] internal
+             *         method of replacer with the argument ToString(i).
+             *      3. If Type(v) is String then let item be v.
+             *      4. Else if Type(v) is Number then let item be ToString(v).
+             *      5. Else if Type(v) is Object then
+             *         a. If the [[Class]] internal property of v is "String"
+             *            or "Number" then let item be ToString(v).
+             *      6. If item is not undefined and item is not currently an
+             *         element of PropertyList then,
+             *         a. Append item to the end of PropertyList.
+             *      7. Let i be i + 1.
+             */
+
+            /* Step 4b(ii). */
+            uint32_t len;
+            JS_ALWAYS_TRUE(GetLengthProperty(cx, replacer, &len));
+            if (replacer->is<ArrayObject>() && !replacer->isIndexed())
+                len = Min(len, replacer->getDenseInitializedLength());
+
+            // Cap the initial size to a moderately small value.  This avoids
+            // ridiculous over-allocation if an array with bogusly-huge length
+            // is passed in.  If we end up having to add elements past this
+            // size, the set will naturally resize to accommodate them.
+            const uint32_t MaxInitialSize = 1024;
+            HashSet<jsid, JsidHasher> idSet(cx);
+            if (!idSet.init(Min(len, MaxInitialSize)))
+                return false;
+
+            /* Step 4b(iii). */
+            uint32_t i = 0;
+
+            /* Step 4b(iv). */
+            RootedValue v(cx);
+            for (; i < len; i++) {
+                if (!CheckForInterrupt(cx))
+                    return false;
+
+                /* Step 4b(iv)(2). */
+                if (!JSObject::getElement(cx, replacer, replacer, i, &v))
+                    return false;
+
+                RootedId id(cx);
+                if (v.isNumber()) {
+                    /* Step 4b(iv)(4). */
+                    int32_t n;
+                    if (v.isNumber() && ValueFitsInInt32(v, &n) && INT_FITS_IN_JSID(n)) {
+                        id = INT_TO_JSID(n);
+                    } else {
+                        if (!ValueToId<CanGC>(cx, v, &id))
+                            return false;
+                    }
+                } else if (v.isString() ||
+                           IsObjectWithClass(v, ESClass_String, cx) ||
+                           IsObjectWithClass(v, ESClass_Number, cx))
+                {
+                    /* Step 4b(iv)(3), 4b(iv)(5). */
+                    if (!ValueToId<CanGC>(cx, v, &id))
+                        return false;
+                } else {
+                    continue;
+                }
+
+                /* Step 4b(iv)(6). */
+                HashSet<jsid, JsidHasher>::AddPtr p = idSet.lookupForAdd(id);
+                if (!p) {
+                    /* Step 4b(iv)(6)(a). */
+                    if (!idSet.add(p, id) || !propertyList.append(id))
+                        return false;
+                }
+            }
+        } else {
+            replacer = nullptr;
+        }
+    }
+
+    /* Step 5. */
+    if (space.isObject()) {
+        RootedObject spaceObj(cx, &space.toObject());
+        if (ObjectClassIs(spaceObj, ESClass_Number, cx)) {
+            double d;
+            if (!ToNumber(cx, space, &d))
+                return false;
+            space = NumberValue(d);
+        } else if (ObjectClassIs(spaceObj, ESClass_String, cx)) {
+            JSString *str = ToStringSlow<CanGC>(cx, space);
+            if (!str)
+                return false;
+            space = StringValue(str);
+        }
+    }
+
+    StringBuffer gap(cx);
+
+    if (space.isNumber()) {
+        /* Step 6. */
+        double d;
+        JS_ALWAYS_TRUE(ToInteger(cx, space, &d));
+        d = Min(10.0, d);
+        if (d >= 1 && !gap.appendN(' ', uint32_t(d)))
+            return false;
+    } else if (space.isString()) {
+        /* Step 7. */
+        JSLinearString *str = space.toString()->ensureLinear(cx);
+        if (!str)
+            return false;
+        JS::Anchor<JSString *> anchor(str);
+        size_t len = Min(size_t(10), space.toString()->length());
+        if (!gap.append(str->chars(), len))
+            return false;
+    } else {
+        /* Step 8. */
+        JS_ASSERT(gap.empty());
+    }
+
+    /* Step 9. */
+    RootedObject wrapper(cx, NewBuiltinClassInstance(cx, &JSObject::class_));
+    if (!wrapper)
+        return false;
+
+    /* Step 10. */
+    RootedId emptyId(cx, NameToId(cx->names().empty));
+    if (!DefineNativeProperty(cx, wrapper, emptyId, vp, JS_PropertyStub, JS_StrictPropertyStub,
+                              JSPROP_ENUMERATE))
+    {
+        return false;
+    }
+
+    /* Step 11. */
+    StringifyContext scx(cx, sb, gap, replacer, propertyList);
+    if (!PreprocessValue(cx, wrapper, HandleId(emptyId), vp, &scx))
+        return false;
+    if (IsFilteredValue(vp))
+        return true;
+
+    return Str(cx, vp, &scx);
+}
+
+/* ES5 15.12.2 Walk. */
+static bool
+Walk(JSContext *cx, HandleObject holder, HandleId name, HandleValue reviver, MutableHandleValue vp)
+{
+    JS_CHECK_RECURSION(cx, return false);
+
+    /* Step 1. */
+    RootedValue val(cx);
+    if (!JSObject::getGeneric(cx, holder, holder, name, &val))
+        return false;
+
+    /* Step 2. */
+    if (val.isObject()) {
+        RootedObject obj(cx, &val.toObject());
+
+        if (ObjectClassIs(obj, ESClass_Array, cx)) {
+            /* Step 2a(ii). */
+            uint32_t length;
+            if (!GetLengthProperty(cx, obj, &length))
+                return false;
+
+            /* Step 2a(i), 2a(iii-iv). */
+            RootedId id(cx);
+            RootedValue newElement(cx);
+            for (uint32_t i = 0; i < length; i++) {
+                if (!IndexToId(cx, i, &id))
+                    return false;
+
+                /* Step 2a(iii)(1). */
+                if (!Walk(cx, obj, id, reviver, &newElement))
+                    return false;
+
+                if (newElement.isUndefined()) {
+                    /* Step 2a(iii)(2). */
+                    bool succeeded;
+                    if (!JSObject::deleteByValue(cx, obj, IdToValue(id), &succeeded))
+                        return false;
+                } else {
+                    /* Step 2a(iii)(3). */
+                    // XXX This definition should ignore success/failure, when
+                    //     our property-definition APIs indicate that.
+                    if (!JSObject::defineGeneric(cx, obj, id, newElement))
+                        return false;
+                }
+            }
+        } else {
+            /* Step 2b(i). */
+            AutoIdVector keys(cx);
+            if (!GetPropertyNames(cx, obj, JSITER_OWNONLY, &keys))
+                return false;
+
+            /* Step 2b(ii). */
+            RootedId id(cx);
+            RootedValue newElement(cx);
+            for (size_t i = 0, len = keys.length(); i < len; i++) {
+                /* Step 2b(ii)(1). */
+                id = keys[i];
+                if (!Walk(cx, obj, id, reviver, &newElement))
+                    return false;
+
+                if (newElement.isUndefined()) {
+                    /* Step 2b(ii)(2). */
+                    bool succeeded;
+                    if (!JSObject::deleteByValue(cx, obj, IdToValue(id), &succeeded))
+                        return false;
+                } else {
+                    /* Step 2b(ii)(3). */
+                    // XXX This definition should ignore success/failure, when
+                    //     our property-definition APIs indicate that.
+                    if (!JSObject::defineGeneric(cx, obj, id, newElement))
+                        return false;
+                }
+            }
+        }
+    }
+
+    /* Step 3. */
+    RootedString key(cx, IdToString(cx, name));
+    if (!key)
+        return false;
+
+    InvokeArgs args(cx);
+    if (!args.init(2))
+        return false;
+
+    args.setCallee(reviver);
+    args.setThis(ObjectValue(*holder));
+    args[0].setString(key);
+    args[1].set(val);
+
+    if (!Invoke(cx, args))
+        return false;
+    vp.set(args.rval());
+    return true;
+}
+
+static bool
+Revive(JSContext *cx, HandleValue reviver, MutableHandleValue vp)
+{
+    RootedObject obj(cx, NewBuiltinClassInstance(cx, &JSObject::class_));
+    if (!obj)
+        return false;
+
+    if (!JSObject::defineProperty(cx, obj, cx->names().empty, vp))
+        return false;
+
+    Rooted<jsid> id(cx, NameToId(cx->names().empty));
+    return Walk(cx, obj, id, reviver, vp);
+}
+
+bool
+js::ParseJSONWithReviver(JSContext *cx, ConstTwoByteChars chars, size_t length,
+                         HandleValue reviver, MutableHandleValue vp)
+{
+    /* 15.12.2 steps 2-3. */
+    JSONParser parser(cx, chars, length);
+    if (!parser.parse(vp))
+        return false;
+
+    /* 15.12.2 steps 4-5. */
+    if (js_IsCallable(reviver))
+        return Revive(cx, reviver, vp);
+    return true;
+}
+
+#if JS_HAS_TOSOURCE
+static bool
+json_toSource(JSContext *cx, unsigned argc, Value *vp)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+    args.rval().setString(cx->names().JSON);
+    return true;
+}
+#endif
+
+/* ES5 15.12.2. */
+static bool
+json_parse(JSContext *cx, unsigned argc, Value *vp)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+
+    /* Step 1. */
+    JSString *str = (args.length() >= 1)
+                    ? ToString<CanGC>(cx, args[0])
+                    : cx->names().undefined;
+    if (!str)
+        return false;
+
+    Rooted<JSFlatString*> flat(cx, str->ensureFlat(cx));
+    if (!flat)
+        return false;
+
+    JS::Anchor<JSString *> anchor(flat);
+
+    RootedValue reviver(cx, args.get(1));
+
+    /* Steps 2-5. */
+    return ParseJSONWithReviver(cx, ConstTwoByteChars(flat->chars(), flat->length()),
+                                flat->length(), reviver, args.rval());
+}
+
+/* ES5 15.12.3. */
+bool
+json_stringify(JSContext *cx, unsigned argc, Value *vp)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+    RootedObject replacer(cx, args.get(1).isObject() ? &args[1].toObject() : nullptr);
+    RootedValue value(cx, args.get(0));
+    RootedValue space(cx, args.get(2));
+
+    StringBuffer sb(cx);
+    if (!js_Stringify(cx, &value, replacer, space, sb))
+        return false;
+
+    // XXX This can never happen to nsJSON.cpp, but the JSON object
+    // needs to support returning undefined. So this is a little awkward
+    // for the API, because we want to support streaming writers.
+    if (!sb.empty()) {
+        JSString *str = sb.finishString();
+        if (!str)
+            return false;
+        args.rval().setString(str);
+    } else {
+        args.rval().setUndefined();
+    }
+
+    return true;
+}
+
+static const JSFunctionSpec json_static_methods[] = {
+#if JS_HAS_TOSOURCE
+    JS_FN(js_toSource_str,  json_toSource,      0, 0),
+#endif
+    JS_FN("parse",          json_parse,         2, 0),
+    JS_FN("stringify",      json_stringify,     3, 0),
+    JS_FS_END
+};
+
+JSObject *
+js_InitJSONClass(JSContext *cx, HandleObject obj)
+{
+    Rooted<GlobalObject*> global(cx, &obj->as<GlobalObject>());
+
+    /*
+     * JSON requires that Boolean.prototype.valueOf be created and stashed in a
+     * reserved slot on the global object; see js::BooleanGetPrimitiveValueSlow
+     * called from PreprocessValue above.
+     */
+    if (!GlobalObject::getOrCreateBooleanPrototype(cx, global))
+        return nullptr;
+
+    RootedObject proto(cx, obj->as<GlobalObject>().getOrCreateObjectPrototype(cx));
+    RootedObject JSON(cx, NewObjectWithClassProto(cx, &JSONClass, proto, global, SingletonObject));
+    if (!JSON)
+        return nullptr;
+
+    if (!JS_DefineProperty(cx, global, js_JSON_str, JSON, 0,
+                           JS_PropertyStub, JS_StrictPropertyStub))
+        return nullptr;
+
+    if (!JS_DefineFunctions(cx, JSON, json_static_methods))
+        return nullptr;
+
+    global->setConstructor(JSProto_JSON, ObjectValue(*JSON));
+
+    return JSON;
+}