dayjs/esm/plugin/devHelper/index.js

/* eslint-disable no-console */
export default (function (o, c, d) {
  /* istanbul ignore next line */
  if (!process || process.env.NODE_ENV !== 'production') {
    var proto = c.prototype;
    var oldParse = proto.parse;

    proto.parse = function (cfg) {
      var date = cfg.date;

      if (typeof date === 'string' && date.length === 13) {
        console.warn("To parse a Unix timestamp like " + date + ", you should pass it as a Number. https://day.js.org/docs/en/parse/unix-timestamp-milliseconds");
      }

      if (typeof date === 'number' && String(date).length === 4) {
        console.warn("Guessing you may want to parse the Year " + date + ", you should pass it as a String " + date + ", not a Number. Otherwise, " + date + " will be treated as a Unix timestamp");
      }

      if (cfg.args.length >= 2 && !d.p.customParseFormat) {
        console.warn("To parse a date-time string like " + date + " using the given format, you should enable customParseFormat plugin first. https://day.js.org/docs/en/parse/string-format");
      }

      return oldParse.bind(this)(cfg);
    };

    var oldLocale = d.locale;

    d.locale = function (preset, object, isLocal) {
      if (typeof object === 'undefined' && typeof preset === 'string') {
        if (!d.Ls[preset]) {
          console.warn("Guessing you may want to use locale " + preset + ", you have to load it before using it. https://day.js.org/docs/en/i18n/loading-into-nodejs");
        }
      }

      return oldLocale(preset, object, isLocal);
    };
  }
});