core-js/modules/es.regexp.to-string.js

'use strict';
var PROPER_FUNCTION_NAME = require('../internals/function-name').PROPER;
var defineBuiltIn = require('../internals/define-built-in');
var anObject = require('../internals/an-object');
var $toString = require('../internals/to-string');
var fails = require('../internals/fails');
var getRegExpFlags = require('../internals/regexp-get-flags');

var TO_STRING = 'toString';
var RegExpPrototype = RegExp.prototype;
var nativeToString = RegExpPrototype[TO_STRING];

var NOT_GENERIC = fails(function () { return nativeToString.call({ source: 'a', flags: 'b' }) !== '/a/b'; });
// FF44- RegExp#toString has a wrong name
var INCORRECT_NAME = PROPER_FUNCTION_NAME && nativeToString.name !== TO_STRING;

// `RegExp.prototype.toString` method
// https://tc39.es/ecma262/#sec-regexp.prototype.tostring
if (NOT_GENERIC || INCORRECT_NAME) {
  defineBuiltIn(RegExpPrototype, TO_STRING, function toString() {
    var R = anObject(this);
    var pattern = $toString(R.source);
    var flags = $toString(getRegExpFlags(R));
    return '/' + pattern + '/' + flags;
  }, { unsafe: true });
}