[00:00] We're back with our canvas node. We've got our read-only properties with our hash. We have a constructor, we have a get position, and we have a move function. We now have a new requirement where we want to be able to modify the position from outside directly. Now this is an issue because if we hover over this,

[00:17] you can see that we cannot assign to position because it's a read-only property. Getters, by default, they are read-only because it just doesn't make sense to assign to a getter like this. Your job is to try to work out what API we need to add to our class in order to make this mutable,

[00:36] and also to try to figure out the logic of what you would even do to kind of figure this out, right? What logic needs to be added to this class in order to actually assign it into these private properties? And I think you're gonna need a setter. Good luck.


Continuing on with the `CanvasNode`, we have some read-only variables `#x` and `#y` along with a constructor, a `position` getter, and a `move` function. Here's our class:

```tsx
class CanvasNode {
  #x: number;
  #y: number;

  constructor(position?: { x: number; y: number }) {
    this.#x = position?.x ?? 0;
    this.#y = position?.y ?? 0;
  }

  get position() {
    return {
      x: this.#x,
      y: this.#y,
    };
  }

  move(x: number, y: number) {
    this.#x = x;
    this.#y = y;
  }
}
```

Now we have a new requirement: the ability to modify the `position` directly from outside the class. 

Currently the `position` is a read-only property, as seen in the test case:

```typescript
// inside the test case
canvasNode.position = { x: 10, y: 20 }; // red squiggly line under position

// Hovering over position shows:
Cannot assign to 'position' because it is a read-only property.
```

Getters are inherently read-only, and it wouldn't make sense to assign a value to a getter anyways.

## Challenge

Your challenge is to determine how to modify the `CanvasNode` class to make the `position` property mutable. Additionally, you'll need to determine the logic required to be added to the class to assign the new value to the private properties.

Hint: look into setters!

Setters are methods that are used to modify properties outside of a class.

[00:00] Okay, so the way that we do this is very similar to this syntax. We basically say set position and Then we take in the thing that is required to set the position So we hover over this a set accessor must have exactly one

[00:16] Parameter that parameter is going to take in the thing that is being set in this case position And now sets a set of functions are super nice in TypeScript because we don't actually need to give this a type It understands what type it's supposed to be from the thing that the getter

[00:33] Returns so nice so this position now We can now say this dot X equals positive X and this dot hash Y equals positive Y Beautiful, this is so so nice and now everything is going to work down the bottom so expect

[00:51] Where is it this one here? This is now no longer read-only It's now just a mutable property because it's got a setter attached to it So this kind of getter and setter logic you might be very used to this from other languages But having it in TypeScript and JavaScript because this is not TypeScript only syntax This is also JavaScript syntax, too

[01:09] And of course this is also available in object syntax, too but having it in classes Again is really nice because you just get a sort of cleaner API and it feels like it sort of belongs in this kind of Classes mindset too. So there we go getters and setters


The syntax for specifying a setter is very similar to the syntax for specifying a getter. The difference is that we use the `set` keyword instead of the `get` keyword.

In this case, the `position` setter will take in an argument for position, which will be an object with `x` and `y` properties:

```typescript
set position(pos) {
  this.#x = pos.x;
  this.#y = pos.y;
}
```

We don't need to explicitly declare the type for the `pos` parameter because TypeScript is smart enough to infer the type based on the getter's return type.

Note that with the setter in place, `position` is no longer read-only. It has transformed into a mutable property equipped with a setter.

The structure of getters and setters may be familiar if you've worked with other languages. It's a great way to encapsulate logic for retrieving and modifying properties.

And that's it- a rundown on implementing getters and setters in TypeScript.


Setters allow you to modify properties outside of a class.

Add a Setter to a TypeScript Class

Setter Methods in TypeScript

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JavaScript vs. TypeScript in the Build Process

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A quick guide to installing Node.js and Visual Studio Code to create a stable environment for web development.

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Installing pnpm for Package Management

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Unexpected Token Error in the Browser

Use the TypeScript CLI to convert a TypeScript file into a JavaScript file.

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Compile TypeScript to JavaScript with the TypeScript CLI

Convert a TypeScript File into a JavaScript File

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Use tsc's Watch Mode to Automatically Compile TypeScript Files

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Compiling TypeScript Files to a Directory

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Create a new project with Vite and TypeScript to improve upon our current setup.

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Use Vite for a Frontend App with TypeScript

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TypeScript as a Linter

Comparing Vite with tsc

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TypeScript in a CI/CD System

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Should TypeScript Block Your Dev Server?

The tsx CLI tool allows you to quickly run scripts written in TypeScript.

Quickly Create Scripts with tsx

TypeScript in The Build Process

Learn how to identify and fix common type errors in your functions.

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Fixing Errors in the `add` Function

Understanding Function Errors

Learn about annotating empty function parameters in TypeScript.

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Annotating Empty Parameters

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TypeScript Basic Types

Basic Types in TypeScript

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Optional Function Parameters in TypeScript

Optional Function Parameters

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Add a Default Parameter with `=`

Default Parameters in JavaScript Functions

Annotate the type of object literals to avoid TypeScript errors and improve inference.

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Annotating with {}

Typing Object Literals

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Specifying Optional Properties

Making Object Property Types Optional

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Creating `type` Aliases

A Single Source of Truth for Type Definitions

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Learn about the two different syntaxes for defining arrays in TypeScript.

Two Syntaxes for Arrays

Add an Array to an Object

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There are few different ways in which an array of objects can be expressed

Representing an Array of Objects

Arrays of Objects in TypeScript

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Using Rest Parameters in TypeScript

Rest Parameters in TypeScript

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Using Tuple Syntax in TypeScript

Tuples for Precise Array Structures in TypeScript

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Working with Optional Tuple Members in TypeScript

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The Controversial `any` Type

How to make sure a function and its parameters and return types fit certain criteria, and how to annotate functions passed as arguments

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Function Types for Type Aliases in TypeScript

Function Types

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The `void` Type

Typing an Event Listener

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Restricting `Set` Types

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Typing Fetch API Responses in Async Functions

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Hovering Over a Function Call

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TSDoc Comments

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The Control + Space Shortcut

Manually Triggering Autocomplete

TypeScript's Approach to Errors

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Quick Renaming in VS Code

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Using Autocomplete and Quick Fix to Import Variables

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The Organize Imports Hotkey in VS Code

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Automatic Code Formatting with Prettier

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Restarting the TypeScript Server in VS Code

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Introducing Union Types in TypeScript

Handling Null Values in TypeScript

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Literal Type Assignability

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Setter Methods in TypeScript

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