Well‑formed JSON.stringify

packages/core-js-compat/src/data.js

@@ -337,6 +337,11 @@ const data = {
     firefox: '65',
     safari: '12.1',
   },
+  'es.json.stringify': {
+    chrome: '72',
+    firefox: '64',
+    safari: '12.1',
+  },
   'es.json.to-string-tag': {
     edge: '15',
     chrome: '50',

packages/core-js-compat/src/modules-by-versions.js

@@ -44,4 +44,7 @@ module.exports = {
     'esnext.map.upsert',
     'esnext.weak-map.upsert',
   ],
+  3.4: [
+    'es.json.stringify',
+  ],
 };

packages/core-js/es/json/stringify.js

@@ -1,6 +1,9 @@
+require('../../modules/es.json.stringify');
 var core = require('../../internals/path');
-var $JSON = core.JSON || (core.JSON = { stringify: JSON.stringify });
 
-module.exports = function stringify(it) { // eslint-disable-line no-unused-vars
-  return $JSON.stringify.apply($JSON, arguments);
+if (!core.JSON) core.JSON = { stringify: JSON.stringify };
+
+// eslint-disable-next-line no-unused-vars
+module.exports = function stringify(it, replacer, space) {
+  return core.JSON.stringify.apply(null, arguments);
 };

packages/core-js/modules/es.json.stringify.js

@@ -0,0 +1,45 @@
+var $ = require('../internals/export');
+var getBuiltIn = require('../internals/get-built-in');
+var fails = require('../internals/fails');
+var IndexedObject = require('../internals/indexed-object');
+
+var $stringify = getBuiltIn('JSON', 'stringify');
+var reg = /[\uD800-\uDFFF]/g;
+var re = /^[\uD800-\uDFFF]$/;
+var low = /^[\uD800-\uDBFF]$/;
+var hi = /^[\uDC00-\uDFFF]$/;
+
+var fix = function (string) {
+  var indexed = IndexedObject(string);
+  var length = indexed.length;
+  var result = '';
+  var i = 0;
+  var point, prev, next;
+  for (; i < length; i++) {
+    point = indexed[i];
+    if (re.test(point)) {
+      prev = i === 0 ? '' : indexed[i - 1];
+      next = i === length - 1 ? '' : indexed[i + 1];
+      if ((low.test(point) && !hi.test(next)) || (hi.test(point) && !low.test(prev))) {
+        result += '\\u' + point.charCodeAt(0).toString(16);
+        continue;
+      }
+    } result += point;
+  } return result;
+};
+
+var FORCED = fails(function () {
+  return $stringify('\uDF06\uD834') !== '"\\udf06\\ud834"'
+    || $stringify('\uDEAD') !== '"\\udead"';
+});
+
+if ($stringify) {
+  // https://github.com/tc39/proposal-well-formed-stringify
+  $({ target: 'JSON', stat: true, forced: FORCED }, {
+    // eslint-disable-next-line no-unused-vars
+    stringify: function stringify(it, replacer, space) {
+      var result = $stringify.apply(null, arguments);
+      return typeof result == 'string' && reg.test(result) ? fix(result) : result;
+    }
+  });
+}

packages/core-js/modules/es.symbol.js

@@ -1,6 +1,7 @@
 'use strict';
 var $ = require('../internals/export');
 var global = require('../internals/global');
+var getBuiltIn = require('../internals/get-built-in');
 var IS_PURE = require('../internals/is-pure');
 var DESCRIPTORS = require('../internals/descriptors');
 var NATIVE_SYMBOL = require('../internals/native-symbol');
@@ -42,8 +43,7 @@ var setInternalState = InternalStateModule.set;
 var getInternalState = InternalStateModule.getterFor(SYMBOL);
 var ObjectPrototype = Object[PROTOTYPE];
 var $Symbol = global.Symbol;
-var JSON = global.JSON;
-var nativeJSONStringify = JSON && JSON.stringify;
+var $stringify = getBuiltIn('JSON', 'stringify');
 var nativeGetOwnPropertyDescriptor = getOwnPropertyDescriptorModule.f;
 var nativeDefineProperty = definePropertyModule.f;
 var nativeGetOwnPropertyNames = getOwnPropertyNamesExternal.f;
@@ -264,30 +264,35 @@ $({ target: 'Object', stat: true, forced: fails(function () { getOwnPropertySymb
 
 // `JSON.stringify` method behavior with symbols
 // https://tc39.github.io/ecma262/#sec-json.stringify
-JSON && $({ target: 'JSON', stat: true, forced: !NATIVE_SYMBOL || fails(function () {
-  var symbol = $Symbol();
-  // MS Edge converts symbol values to JSON as {}
-  return nativeJSONStringify([symbol]) != '[null]'
-    // WebKit converts symbol values to JSON as null
-    || nativeJSONStringify({ a: symbol }) != '{}'
-    // V8 throws on boxed symbols
-    || nativeJSONStringify(Object(symbol)) != '{}';
-}) }, {
-  stringify: function stringify(it) {
-    var args = [it];
-    var index = 1;
-    var replacer, $replacer;
-    while (arguments.length > index) args.push(arguments[index++]);
-    $replacer = replacer = args[1];
-    if (!isObject(replacer) && it === undefined || isSymbol(it)) return; // IE8 returns string on undefined
-    if (!isArray(replacer)) replacer = function (key, value) {
-      if (typeof $replacer == 'function') value = $replacer.call(this, key, value);
-      if (!isSymbol(value)) return value;
-    };
-    args[1] = replacer;
-    return nativeJSONStringify.apply(JSON, args);
-  }
-});
+if ($stringify) {
+  var FORCED_JSON_STRINGIFY = !NATIVE_SYMBOL || fails(function () {
+    var symbol = $Symbol();
+    // MS Edge converts symbol values to JSON as {}
+    return $stringify([symbol]) != '[null]'
+      // WebKit converts symbol values to JSON as null
+      || $stringify({ a: symbol }) != '{}'
+      // V8 throws on boxed symbols
+      || $stringify(Object(symbol)) != '{}';
+  });
+
+  $({ target: 'JSON', stat: true, forced: FORCED_JSON_STRINGIFY }, {
+    // eslint-disable-next-line no-unused-vars
+    stringify: function stringify(it, replacer, space) {
+      var args = [it];
+      var index = 1;
+      var $replacer;
+      while (arguments.length > index) args.push(arguments[index++]);
+      $replacer = replacer;
+      if (!isObject(replacer) && it === undefined || isSymbol(it)) return; // IE8 returns string on undefined
+      if (!isArray(replacer)) replacer = function (key, value) {
+        if (typeof $replacer == 'function') value = $replacer.call(this, key, value);
+        if (!isSymbol(value)) return value;
+      };
+      args[1] = replacer;
+      return $stringify.apply(null, args);
+    }
+  });
+}
 
 // `Symbol.prototype[@@toPrimitive]` method
 // https://tc39.github.io/ecma262/#sec-symbol.prototype-@@toprimitive

tests/compat/tests.js

@@ -439,6 +439,10 @@ GLOBAL.tests = {
   'es.global-this': function () {
     return globalThis;
   },
+  'es.json.stringify': function () {
+    return JSON.stringify('\uDF06\uD834') === '"\\udf06\\ud834"'
+      && JSON.stringify('\uDEAD') === '"\\udead"';
+  },
   'es.json.to-string-tag': [SYMBOLS_SUPPORT, function () {
     return JSON[Symbol.toStringTag];
   }],

tests/pure/es.json.stringify.js

@@ -0,0 +1,16 @@
+import { GLOBAL } from '../helpers/constants';
+import stringify from 'core-js/es/json/stringify';
+
+if (GLOBAL.JSON) {
+  QUnit.test('Well‑formed JSON.stringify', assert => {
+    assert.isFunction(stringify);
+    assert.arity(stringify, 3);
+    assert.name(stringify, 'stringify');
+
+    assert.same(stringify({ foo: 'bar' }), '{"foo":"bar"}', 'basic');
+    assert.same(stringify('\uDEAD'), '"\\udead"', 'r1');
+    assert.same(stringify('\uDF06\uD834'), '"\\udf06\\ud834"', 'r2');
+    assert.same(stringify('\uDF06ab\uD834'), '"\\udf06ab\\ud834"', 'r3');
+    assert.same(stringify('𠮷'), '"𠮷"', 'r4');
+  });
+}

tests/pure/index.js

@@ -35,6 +35,7 @@ import './es.date.to-json';
 import './es.function.bind';
 import './es.function.has-instance';
 import './es.global-this';
+import './es.json.stringify';
 import './es.map';
 import './es.math.acosh';
 import './es.math.asinh';

tests/tests/es.json.stringify.js

@@ -0,0 +1,17 @@
+import { GLOBAL } from '../helpers/constants';
+
+if (GLOBAL.JSON) {
+  QUnit.test('Well‑formed JSON.stringify', assert => {
+    const { stringify } = JSON;
+    assert.isFunction(stringify);
+    assert.arity(stringify, 3);
+    assert.name(stringify, 'stringify');
+    assert.looksNative(stringify);
+
+    assert.same(stringify({ foo: 'bar' }), '{"foo":"bar"}', 'basic');
+    assert.same(stringify('\uDEAD'), '"\\udead"', 'r1');
+    assert.same(stringify('\uDF06\uD834'), '"\\udf06\\ud834"', 'r2');
+    assert.same(stringify('\uDF06ab\uD834'), '"\\udf06ab\\ud834"', 'r3');
+    assert.same(stringify('𠮷'), '"𠮷"', 'r4');
+  });
+}

tests/tests/index.js

@@ -35,6 +35,7 @@ import './es.function.bind';
 import './es.function.has-instance';
 import './es.function.name';
 import './es.global-this';
+import './es.json.stringify';
 import './es.map';
 import './es.math.acosh';
 import './es.math.asinh';