Add __proto__ to objects and arrays

CHANGELOG.md

@@ -3,6 +3,9 @@
 [c-unreleased]: https://github.com/json5/json5/tree/main
 [d-unreleased]: https://github.com/json5/json5/compare/v2.2.1...HEAD
 
+- Fix: Properties with the name `__proto__` are added to objects and arrays.
+  ([#199])
+
 ### v2.2.1 [[code][c2.2.1], [diff][d2.2.1]]
 
 [c2.2.1]: https://github.com/json5/json5/tree/v2.2.1
@@ -360,6 +363,7 @@ parser for the regular JSON format.
 [#182]: https://github.com/json5/json5/issues/182
 [#187]: https://github.com/json5/json5/issues/187
 [#196]: https://github.com/json5/json5/issues/196
+[#199]: https://github.com/json5/json5/issues/199
 [#208]: https://github.com/json5/json5/issues/208
 [#210]: https://github.com/json5/json5/issues/210
 [#222]: https://github.com/json5/json5/issues/222

lib/parse.js

@@ -42,12 +42,34 @@ module.exports = function parse (text, reviver) {
 function internalize (holder, name, reviver) {
     const value = holder[name]
     if (value != null && typeof value === 'object') {
-        for (const key in value) {
-            const replacement = internalize(value, key, reviver)
-            if (replacement === undefined) {
-                delete value[key]
-            } else {
-                value[key] = replacement
+        if (Array.isArray(value)) {
+            for (let i = 0; i < value.length; i++) {
+                const key = String(i)
+                const replacement = internalize(value, key, reviver)
+                if (replacement === undefined) {
+                    delete value[key]
+                } else {
+                    Object.defineProperty(value, key, {
+                        value: replacement,
+                        writable: true,
+                        enumerable: true,
+                        configurable: true,
+                    })
+                }
+            }
+        } else {
+            for (const key in value) {
+                const replacement = internalize(value, key, reviver)
+                if (replacement === undefined) {
+                    delete value[key]
+                } else {
+                    Object.defineProperty(value, key, {
+                        value: replacement,
+                        writable: true,
+                        enumerable: true,
+                        configurable: true,
+                    })
+                }
             }
         }
     }
@@ -973,7 +995,12 @@ function push () {
         if (Array.isArray(parent)) {
             parent.push(value)
         } else {
-            parent[key] = value
+            Object.defineProperty(parent, key, {
+                value,
+                writable: true,
+                enumerable: true,
+                configurable: true,
+            })
         }
     }
 

test/parse.js

@@ -48,6 +48,13 @@ t.test('parse(text)', t => {
             'parses escaped property names'
         )
 
+        t.strictSame(
+            // eslint-disable-next-line no-proto
+            JSON5.parse('{"__proto__":1}').__proto__,
+            1,
+            'preserves __proto__ property names'
+        )
+
         t.strictSame(
             JSON5.parse('{abc:1,def:2}'),
             {abc: 1, def: 2},