old_contents: import { normalizeObjectUnits } from '../units/aliases';
  import { getLocale } from '../locale/locales';
  import isDurationValid from './valid.js';
  
  export function Duration (duration) {
      var normalizedInput = normalizeObjectUnits(duration);
  
      this._isValid = isDurationValid(normalizedInput);
      this.isValid = () => this._isValid;
  
      var years = this._isValid && normalizedInput.year || 0,
          quarters = this._isValid && normalizedInput.quarter || 0,
          months = this._isValid && normalizedInput.month || 0,
          weeks = this._isValid && normalizedInput.week || 0,
          days = this._isValid && normalizedInput.day || 0,
          hours = this._isValid && normalizedInput.hour || 0,
          minutes = this._isValid && normalizedInput.minute || 0,
          seconds = this._isValid && normalizedInput.second || 0,
          milliseconds = this._isValid && normalizedInput.millisecond || 0;
  
      // representation for dateAddRemove
      this._milliseconds = +milliseconds +
          seconds * 1e3 + // 1000
          minutes * 6e4 + // 1000 * 60
          hours * 1000 * 60 * 60; //using 1000 * 60 * 60 instead of 36e5 to avoid floating point rounding errors https://github.com/moment/moment/issues/2978
      // Because of dateAddRemove treats 24 hours as different from a
      // day when working around DST, we need to store them separately
      this._days = +days +
          weeks * 7;
      // It is impossible translate months into days without knowing
      // which months you are are talking about, so we have to store
      // it separately.
      this._months = +months +
          quarters * 3 +
          years * 12;
  
      this._data = {};
  
      this._locale = getLocale();
  
      this._bubble();
  }
  
  export function isDuration (obj) {
      return obj instanceof Duration;
  }
  
new_contents: import { normalizeObjectUnits } from '../units/aliases';
  import { getLocale } from '../locale/locales';
  import isDurationValid from './valid.js';
  
  export function Duration (duration) {
      var normalizedInput = normalizeObjectUnits(duration);
  
      this._isValid = isDurationValid(normalizedInput);
      this.isValid = function () {
          return this._isValid;
      };
  
      var years = this._isValid && normalizedInput.year || 0,
          quarters = this._isValid && normalizedInput.quarter || 0,
          months = this._isValid && normalizedInput.month || 0,
          weeks = this._isValid && normalizedInput.week || 0,
          days = this._isValid && normalizedInput.day || 0,
          hours = this._isValid && normalizedInput.hour || 0,
          minutes = this._isValid && normalizedInput.minute || 0,
          seconds = this._isValid && normalizedInput.second || 0,
          milliseconds = this._isValid && normalizedInput.millisecond || 0;
  
      // representation for dateAddRemove
      this._milliseconds = +milliseconds +
          seconds * 1e3 + // 1000
          minutes * 6e4 + // 1000 * 60
          hours * 1000 * 60 * 60; //using 1000 * 60 * 60 instead of 36e5 to avoid floating point rounding errors https://github.com/moment/moment/issues/2978
      // Because of dateAddRemove treats 24 hours as different from a
      // day when working around DST, we need to store them separately
      this._days = +days +
          weeks * 7;
      // It is impossible translate months into days without knowing
      // which months you are are talking about, so we have to store
      // it separately.
      this._months = +months +
          quarters * 3 +
          years * 12;
  
      this._data = {};
  
      this._locale = getLocale();
  
      this._bubble();
  }
  
  export function isDuration (obj) {
      return obj instanceof Duration;
  }
  
subject: Replace arrow function