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

Standard library

var DatePrototype = Date.prototype;
var INVALID_DATE = 'Invalid Date';
var TO_STRING = 'toString';
var nativeDateToString = DatePrototype[TO_STRING];
var getTime = DatePrototype.getTime;

// `Date.prototype.toString` method
// https://tc39.github.io/ecma262/#sec-date.prototype.tostring
if (new Date(NaN) + '' != INVALID_DATE) {
  require('../internals/redefine')(DatePrototype, TO_STRING, function toString() {
    var value = getTime.call(this);
    // eslint-disable-next-line no-self-compare
    return value === value ? nativeDateToString.call(this) : INVALID_DATE;
  });
}