[00:00] Now that we've got our getter for this position here, you might think, okay, now we don't need the outside to be able to access or modify X and Y here. That's really important. So getPosition is kind of like our external API for this and this stuff, the X and Y number,

[00:18] are both the internal API. We don't want these to be exposed to the outside. So I've got a test there, which is basically saying, should not be able to access X and Y from the outside, and it's expecting an error when you try to access either X or Y, but currently we're not able to do that.

[00:36] Your job is to try to figure out how to make that possible. There is actually two ways of doing this. There is a JavaScript-first way and there is a TypeScript-first way. I would prefer the JavaScript-first way, I think, but I'll forgive you whichever solution you find and good luck if you can find both.

In our `CanvasNode` class, we have implemented a `position` getter as our means for accessing node coordinates:

```typescript
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,
    };
  }
  // ...
}
```

However, we need to make sure that external manipulation of `x` and `y` is not allowed.

These properties should only be internal, but they are currently still accessible from outside the class as seen in the test case:

```typescript
it("Should not be able to access x and y from the outside", () => {
  const canvasNode = new CanvasNode();

  // @ts-expect-error // squiggly line under @ts-expect-error
  canvasNode.x;
  // @ts-expect-error // squiggly line under @ts-expect-error
  canvasNode.y;
});
```

## Challenge

Your task is to resolve this issue by blocking awareness and access to `x` and `y` from outside the `CanvasNode` class.

There are two potential approaches for this: one that's JavaScript-first and one that's TypeScript-first. The JavaScript-first approach is preferred, but either solution is acceptable. See if you can find both!

Learn two methods to hide internal variables in classes.

[00:00] Let's look at the TypeScript first way first. The TypeScript first way basically introduces a new keyword into TypeScript or into JavaScript to describe these attributes. And we can say private X and private Y. These aren't people in the army.

[00:18] This is describing whether this is a public property or a private property. If I wanted this to be public, I could just say public Y and public is the default too. So we get private X and private Y. And now when we try to access them from the outside, you can see that it is private and can only be accessible within class CanvasNode.

[00:39] That's pretty cool. But this is like a TypeScript only thing. This means if we ever need to refactor our code to JavaScript, like it would be great if this worked at runtime. It turns out there is a language feature we can use for this too, which is to add a and what is this a hash? God, I lost my brain for a second there.

[00:58] A hash in front of X and Y. And now this means that you, without needing to add any separate annotations, by just using this hash inside a class, you can see that we get this dot hash X equals position this. And it means now that we can't access, we can't access X on this, of course,

[01:17] but we also can't access hash X either. So property hash X is not accessible outside class CanvasNode because it has a private identifier. So that hash is a private identifier. Super nice. So I would always recommend choosing the JavaScript first way of doing things.

[01:36] And so this, I think, is the correct solution for us, meaning that we can actually just use a JavaScript like built in syntax, which is like part of how browsers and how the language works, essentially, and not relying on a TypeScript only syntax for this.

As mentioned in the introduction to this exercise, there are two ways to prevent access to private properties in classes.

Let's start by looking at the TypeScript-first approach.

## TypeScript-First Approach

This approach introduces the `private` keyword to describe the attributes:

```typescript
class CanvasNode {
  private x: number;
  private y: number;

  ...
```

If you wanted the properties to be public, you could use the `public` keyword. This is the default behavior, so you can leave it out.

Now when trying to access the private properties from outside of the class, TypeScript will display an error:

```typescript
const canvasNode = new CanvasNode();
canvasNode.x; // red squiggly line under x

// Hovering over x shows:
Property 'x' is private and only accessible within class 'CanvasNode'.
```

The `private` keyword works great, but is only available for TypeScript.

## JavaScript-First Approach

The syntax we can use to achieve the same result: adding a hash (`#`) in front of the property names:

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

  ...
```

Like before, this change will cause an error when trying to access the private properties from outside of the class.

What's nice about this approach is that it's a JavaScript feature, so it will work in both TypeScript and JavaScript. This means that if you ever need to refactor your code to JavaScript, it will still work.

There is a TypeScript-first and JavaScript-first approach to preventing access to private properties in classes.

Prevent Access to Private Properties in Classes

Public and Private Properties in TypeScript

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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

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Comparing Vite with tsc

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Quickly Create Scripts with tsx

TypeScript in The Build Process

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Two Syntaxes for Arrays

Add an Array to an Object

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Representing an Array of Objects

Arrays of Objects in TypeScript

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Rest Parameters in TypeScript

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Tuples for Precise Array Structures in TypeScript

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The `void` Type

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Hovering Over a Function Call

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TSDoc Comments

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The Organize Imports Hotkey in VS Code

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Public and Private Properties in TypeScript

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