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

'use strict';
var $ = require('../internals/export');
var getBuiltIn = require('../internals/get-built-in');
var apply = require('../internals/function-apply');
var call = require('../internals/function-call');
var uncurryThis = require('../internals/function-uncurry-this');
var fails = require('../internals/fails');
var isCallable = require('../internals/is-callable');
var isSymbol = require('../internals/is-symbol');
var arraySlice = require('../internals/array-slice');
var getReplacerFunction = require('../internals/get-json-replacer-function');
var NATIVE_SYMBOL = require('../internals/symbol-constructor-detection');

var $String = String;
var $stringify = getBuiltIn('JSON', 'stringify');
var exec = uncurryThis(/./.exec);
var charAt = uncurryThis(''.charAt);
var charCodeAt = uncurryThis(''.charCodeAt);
var replace = uncurryThis(''.replace);
var numberToString = uncurryThis(1.1.toString);

var tester = /[\uD800-\uDFFF]/g;
var low = /^[\uD800-\uDBFF]$/;
var hi = /^[\uDC00-\uDFFF]$/;

var WRONG_SYMBOLS_CONVERSION = !NATIVE_SYMBOL || fails(function () {
  var symbol = getBuiltIn('Symbol')('stringify detection');
  // 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)) !== '{}';
});

// https://github.com/tc39/proposal-well-formed-stringify
var ILL_FORMED_UNICODE = fails(function () {
  return $stringify('\uDF06\uD834') !== '"\\udf06\\ud834"'
    || $stringify('\uDEAD') !== '"\\udead"';
});

var stringifyWithSymbolsFix = function (it, replacer) {
  var args = arraySlice(arguments);
  var $replacer = getReplacerFunction(replacer);
  if (!isCallable($replacer) && (it === undefined || isSymbol(it))) return; // IE8 returns string on undefined
  args[1] = function (key, value) {
    // some old implementations (like WebKit) could pass numbers as keys
    if (isCallable($replacer)) value = call($replacer, this, $String(key), value);
    if (!isSymbol(value)) return value;
  };
  return apply($stringify, null, args);
};

var fixIllFormed = function (match, offset, string) {
  var prev = charAt(string, offset - 1);
  var next = charAt(string, offset + 1);
  if ((exec(low, match) && !exec(hi, next)) || (exec(hi, match) && !exec(low, prev))) {
    return '\\u' + numberToString(charCodeAt(match, 0), 16);
  } return match;
};

if ($stringify) {
  // `JSON.stringify` method
  // https://tc39.es/ecma262/#sec-json.stringify
  $({ target: 'JSON', stat: true, arity: 3, forced: WRONG_SYMBOLS_CONVERSION || ILL_FORMED_UNICODE }, {
    // eslint-disable-next-line no-unused-vars -- required for `.length`
    stringify: function stringify(it, replacer, space) {
      var args = arraySlice(arguments);
      var result = apply(WRONG_SYMBOLS_CONVERSION ? stringifyWithSymbolsFix : $stringify, null, args);
      return ILL_FORMED_UNICODE && typeof result == 'string' ? replace(result, tester, fixIllFormed) : result;
    }
  });
}