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Why use Getters and Setters functions

zellwk profile image Zell Liew 🤗 Originally published at zellwk.com ・4 min read

Getter and Setter functions are collectively known as accessor functions. In my previous two articles, I talked about how I created mix because I wanted to use Getter and Setter functions.

But why do we even use Getters and Setters in the first place?

Why use getters and setters?

I have two reasons.

  1. Syntax reasons
  2. Encapsulation

Syntax reasons

When you try to get the length of an array, you write array.length. This length property acts like a Getter function. It returns values to you in real-time.

If length is a simple property, length will remain no matter how many items you add to the array. Since length changes value depending on the length of the array, it proves that length is NOT a simple property.

I'm not sure whether length is a Getter function though. It wasn't documented anywhere, but I suspect it is.

Since we use array.length (which acts like a Getter function) to get values, why don't we use other Getter functions to get values too? We're already familiar with this syntax.

For example, let's say you have a carousel and you want to get the current slide. You have two options:

  1. Create a normal function
  2. Create a getter function

Here's what the code would look like:

const carousel = {
  // Option 1: Normal function
  getCurrentSlide () {/* ... */},

  // Option 2: Getter function
  get currentSlide () {/* ...*/}
}

First, you can see there's no extra work to define a Getter function. So, why not create one?

Second, if you use a Getter function, you use it by calling the property. If you use a normal function, you need to call the method by writing parenthesis.

// Normal function
const currentSlide = carousel.getCurrentSlide()

// Getter function
const currentSlide = carousel.currentSlide

I think the Getter function version is neater, terser, and easier to understand. It makes more sense to me.

On the flip side, we can also use Setter functions instead of normal functions.

// Normal function
carousel.setCurrentSlide(4)

// Setter function
carousel.currentSlide = 4 // Uses a Setter function

Again, the Setter function version looks neater to me. I'm already used to this syntax because I'm used to assigning values with =.

Now, the key is the use Getter and Setter functions to communicate the code's intent.

  • Getters get something
  • Setters set something
  • Methods do the rest

Once you get this set of intent down, code written with Getter and Setter functions will become easier to parse.

Here's an example where we get a value, set a value, and run a process – all done with functions.

const value = object.getValue() // Gets value
object.setValue(5) // Sets value
object.method() // Runs a process

And here's the same version with Getter and Setter functions.

const value = object.value // Getter
object.value = 5 // Setter 
object.method() // Runs a method

Which is clearer to you? To me, the Getter and Setter version is.

When you use Getter and Setters, it becomes easier to see whether that line of code is GETTING a value, CHANGING a value, or RUNNING a process. You don't even have to pay attention to the specifics of what you wrote.

Yes, it's a small thing. But small things add up. When it adds up, it saves major brainpower.

Encapsulation

The second reason is the ability to create safe code.

Let's say you have a Car. A Car has fuel. When the car leaves the factory, it has 50 litres of fuel.

function Car () {
  const fuel = 50
}

Cars need to know how much fuel they have left. One way is to expose the entire fuel property.

function Car () {
  const fuel = 50
  return {
    fuel
  }
}

const car = Car() 
console.log(car.fuel) // 50

But when you expose the fuel property this way, we allow users to make changes to fuel without limits.

Let's say the car's fuel capacity is 100. They can add any amount and break the car.

car.fuel = 3000
console.log(car.fuel) // 3000

If you used a Getter function, they won't be able to change this fuel property.

function Car () {
  const fuel = 50
  return {
    get fuel () { return fuel } 
  }
}

const car = Car() 
car.fuel = 3000
console.log(car.fuel) // 50

Let's push this further.

If you used a Setter function for fuel, you can create a safeguard for the possible limits. Here's one where we make sure the car's fuel never exceeds 100.

function Car () {
  let fuel = 50
  return {
    get fuel () { return fuel } 
    set fuel (value) {
      fuel = value
      if (value > 100) fuel = 100
    }
  }
}

const car = Car()
car.fuel = 3000
console.log(car.fuel) // 100

In short, I like Getter and Setter functions because of two reasons:

  1. Syntax reasons. It's easier and faster to read code created with accessor functions
  2. Encapsulation. I can create safer code with accessor functions.

That's it!


Thanks for reading. This article was originally posted on my blog. Sign up for my newsletter if you want more articles to help you become a better frontend developer.

Posted on by:

zellwk profile

Zell Liew 🤗

@zellwk

Frontend consultant; teaching frontend to self-taught devs at http://zellwk.com. Currently attempting to demystify Javascript at http://learnjavascript.today.

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