OOP air conditioner model

Question

I had a phone interview and we shared a screen to do a simple challenge. Instructions were ambiguous but I basically had to implement how an air conditioner would work in general. I wrote the following as I talked it out with the interviewer.

So I made a class with a parameter that would be a room temp and then added two properties, heatingSystem and coolingSystem and set them as booleans. Then wrote a function called setTemperature that should’ve been a while loop that changes the temperature and setting of the A/C until it reaches the set temperature.

class AirConditioner {
 constructor(temperature) {
 this.temperature = temperature;
 this.coolingSystem = false;
 this.heatingSystem = false;
 }
 temperatureSet(temperature) {
 while (this.temperature != temperature) {
 if (this.temperature < temperature) {
 // turn on the cooling system and turn off heating system
 if (this.coolingSystem) {
 this.coolingSystem = false;
 this.heatingSystem = true;
 this.temperature++;
 } else {
 this.heatingSystem = true;
 console.log('Temperature has been lowered to ' + this.temperature);
 this.temperature++;
 }
 } else if (this.temperature > temperature) {
 // turn off the cooling system and turning the heating
 if (this.heatingSystem) {
 this.coolingSystem = true;
 this.heatingSystem = false;
 console.log('Temperature has been increased to ' + this.temperature);
 this.temperature--;
 } else {
 this.coolSystem = true;
 console.log('Temperature has been lowered to ' + this.temperature);
 this.temperature--;
 }
 } else {
 // turn off cooling/heating system but keep the fan un
 console.log('temp is the same')
 }
 }
 console.log(`this.temperature: ${this.temperature} temperature: ${temperature}`)
 }
}
const AC = new AirConditioner(78);
console.log(AC);
AC.temperatureSet(63);
console.log(AC);

I honestly don't like the code and can already see a lot of possibilities on how to refactor or add other functions for re-usability. I was wondering what your suggestions are.

• Aaron Goldsmith: Was it a requirement for the interview that you use OOP?

Answer 1

I don't know the position you were interviewed for. Below is the embedded engineer point of view.

• A room temp is not a class parameter. The AC cannot control it directly, so this.temperature++ and this.temperature-- are incorrect. The AC may only read the temp sensor.

• The desired temperature OTOH is a class parameter. You should go an extra mile and provide the interface to set it. BTW, I'd expect temperatureSet to do just that: set the desired temperature.

• As implemented, the program terminates as soon as a certain temperature is reached. I expect an AC system to run more or less forever.

• In the if (this.temperature < temperature) clause you turn on heater no matter what. Move the this.heatingSystem = true; line outside of this.coolingSystem clause.

Assuming the above recommendations are implemented, the basic functionality should look like this:

 while(true) {
 ambientTemperature = this.temperatureSensor.read();
 if (ambientTemperature < this.targetTemperature) {
 if (this.coolingSystem) {
 this.coolingSystem = false;
 } else {
 console.log('Temperature has been lowered to ' + ambientTemperature);
 }
 this.heatingSystem = true;
 } else {
 ....

Of course there is a plenty of room to improve, but again that depends on interviewer expectations, and the AC schematics you'd agree upon.

• Raystafarian: I really like the way you did this answer, tying it directly to the HVAC.
• Flater: Given the nature of having to switch off the cooling boolean when the heating boolean is enabled, it might be better to simply use an int with 3 states so you don't have to set two values at the same time (and risk going out of sync when you make a mistake). Or, alternatively, calculate needsHeating and needsCooling on the fly (by comparing the temperatures)