text: /* 'use strict' 
  --> this make the testing more vigorous, 
      there are certain allowances in non strict mode that will not throw errors.  
  */
  'use strict';
  
  function Thermostat() {
    this.MAX_TEMP_POWER_SAVING_ON = 25;
    this.MINIMUM_TEMPERATURE = 10;
    this.temperature = 20;
  };
  
  Thermostat.prototype.up = function () {
    this.temperature ++;
  };
  
  Thermostat.prototype.down = function () {
    if (this.temperature > this.MINIMUM_TEMPERATURE)
      this.temperature --;
  };
  
  Thermostat.prototype.powerSavingOn = function () {
    if (this.temperature < this.MAX_TEMP_POWER_SAVING_ON)
      this.temperature ++;
  };