Help understanding Getter/Setter a little more

JavaScript
1

Tell us what’s happening:

I was able to solve the problem laid out in this lesson with little issue, but I what I’m having trouble with is understanding the Set portion where celsius is converted to fahrenheit. I don’t know to get this program to work the other way around. I see how it works for F - C. I’m assuming that it does since “temperature()” is set to the conversion formula for C - F.

Your code so far


// Only change code below this line
class Thermostat {
constructor(fahrenheit) {
  this.fahrenheit = fahrenheit;
}

get temperature() {
  return (5 / 9) * (this.fahrenheit - 32);
}

set temperature(celsius) {
  this.fahrenheit = (celsius * 9.0) / 5 + 32;
}
}
// Only change code above this line

const thermos = new Thermostat(76); // Setting in Fahrenheit scale
let temp = thermos.temperature; // 24.44 in Celsius
thermos.temperature = 26;
temp = thermos.temperature; // 26 in Celsius

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User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/86.0.4240.183 Safari/537.36.

Challenge: Use getters and setters to Control Access to an Object

Link to the challenge:

2

The Thermostat is created with a temperature in Fahrenheit, so the “internal” temperature of thermos is stored in Fahrenheit.
The getter and setter methods however work in Celsius.
If you use get temperature(), it’ll convert the internal temperature from Fahrenheit to Celsius and return it.
If you use set temperature(26), it’ll convert the Celsius value to Fahrenheit and store it in this.fahrenheit.

If you want to swap the units, the constructor would be called with a value in Celsius and store it in this.celsius, the getter would have to return a Fahrenheit value, and the setter should take a value in Fahrenheit, convert it and store it in this.celsius.

3

I’m honestly still lost. How do I call the constructor? Using set temperature(26) just throws an error. Would I also need to rewrite this.celcius into the program? To me, that would mean just rewritting the program to accept celsius instead of fahrenheit still leaving me in the same situation.

4

Constructor is a function that is used to set an initial value to the variables of class for example let say i have class Car which contains a variable color and i don’t know which color to choose right now i would rather choose it when i decide to actually make an object of Car. So i make a constructor to do this.

class Car {
     var color;
     constructor(choosenColor){
        this.color=choosenColor;
      }
}

Now my class is ready now when i want to make an object of this class Car and i want it to be Black. Here’s what i’ll do:
const myCoolCar = new Car("Black");
This is how you call a constructor. A constructor gets called when you make an object of it.
So in the challenge this is where the constructor is getting called:

This makes an object thermos of class Thermostat and passes 76 to its constructor which just takes this value and give it to the variable fahrenheit.

5

Okay, this helps me understand better where everything is going. I added this.celcius to my code and it now displays both F and C in the console:

get temperature() {
return this.celsius = (5 / 9) * (this.fahrenheit - 32);
}

set temperature(celsius) {
return this.fahrenheit = (celsius * 9.0) / 5 + 32;
}

//Console reads:
{ fahrenheit: 76, celsius: 24.444444444444446 }

I can manipulate the values going from one to the other using:

//Fahrenheit to Celsius
const thermos = new Thermostat(76);
let temp = thermos.temperature;

//Celisus to Fahrenheit
thermos.temperature = 26;
temp = thermos.temperature;

6

I might have misunderstood you, but you said you’d like to “make the program work the other way around”. I assumed you’d like to make it so that the getters and setters work with Fahrenheit. There’s two ways to do that - it depends on which unit you’d like to use for the internal storage (stored in this.fahrenheit or this.celsius) of the temperature:

  1. The constructor uses Celsius, the getters/setters work with Fahrenheit:
class Thermostat {
constructor(celsius) {
  this.celsius = celsius;
}

get temperature() {
  let fahrenheit =  (this.celsius * 9.0) / 5 + 32;
  return fahrenheit;
}

set temperature(fahrenheit) {
  this.celsius = (5 / 9) * (fahrenheit - 32);
}
}
  1. The constructor uses Fahrenheit, and the getters/setters work with Fahrenheit, too:
class Thermostat {
constructor(fahrenheit) {
  this.fahrenheit = fahrenheit;
}

get temperature() {
  return this.fahrenheit;
}

set temperature(fahrenheit) {
  this.fahrenheit = fahrenheit
}
}

Does that shed some light?

7

This did shed some light and I do have a better grasp at what’s going on.
I probably did ask the wrong question initially (trying to get better at asking more concise questions, I tend to ramble).

I figured what you were saying was to rewrite the program so that it accepts celsius to convert to fahrenheit. I should have asked if this particular program in the lesson was meant to work in both directions without rewriting.

8

I think the point of the exercise (or one point) to take away is this:

  • the internal temperature value is in Fahrenheit, and stored in this.fahrenheit
  • once the Thermostat is “created” with let thermos = new Thermostat(fahrenheit), the interface that a user can interact with (=getters and setters) work entirely in Celsius

The point of the exercise is not to show how a unit converter Fahrenheit-Celsius (and backwards) would work. That’s something entirely different.

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