[00:00] Let's put our hover skills to the test. Here we have a very simple piece of code where we're grabbing an element by document.getElementById and we're expecting to grab an element by ID of 12. But for some reason, we're getting an error here. That's no fun. So what I'd like you to do is investigate

[00:17] what type document.getElementById actually requires and then also, just for a little bonus one, check what type element is too. Good luck.

Put your hover skills to the test to investigate a simple piece of code that's causing an error.

In this code snippet we're trying to grab an element using `document.getElementById` with an ID of `12`. However, something's not working as expected.

```javascript
let element = document.getElementById(12); // red squiggly line under 12
```

How can hovering help to determine what `document.getElementById` actually requires? What type is `element`?


Hovering over a function call can give hints about what arguments a function requires.

[00:00] Okay, so hovers can help here in a bunch of different ways. First of all, we can hover over the error itself here, and this will actually tell us what's going on. Argument of type string or number is not assignable to parameter of type string. And we'll even here get a readout of this getElementById here.

[00:17] So what's happening is if we look at this, you may know like just off the top of your head that getElementById requires a string, great. But if you weren't sure, and let's say this was an external library that you'd really never used before, just hover over getElementById, and you can see it's a method, first of all,

[00:35] and we've got document.getElementById, and the element ID it requires is a string. So it requires string. So just by seeing that red line and actually just doing a bit of contextual hovering, we don't even need to read the error message, which is amazing. And the thing that it returns here is HTML element or null.

[00:55] So that's what that means. So this is what this element is, HTML element or null. Very cool. So we know now, given that we can just sort of scan over all of this stuff, and by the way, the other thing that we didn't hover is documents, var documents, documents. And you notice with the stuff that comes from the DOM, we actually get a little MDN reference here

[01:14] that we can go and click to. We can just go and see the MDN reference for this thing, in this case, which is documents, which is the globally available document thing that you can add stuff to to do some DOM manipulation. So in order to fix this, we just change this to a string, and now everything's happy. Beautiful.


Hovering can help us understand and resolve errors in various ways.

First of all, we can hover over the red squiggly error itself. In this case, hovering over `12`, we get the following error message:

```typescript
Argument of type 'number' is not assignable to parameter of type 'string'.
```

We'll also get a read out of the `getElementById` function:

```typescript
(method) Document.getElementById(elementId: string): HTMLElement | null
```

In the case of `getElementById`, we can see that it requires a string as an argument, and it returns an `HTMLElement` or `null`.

This tells us that we can fix the error by changing the argument to a string:

```typescript
let element = document.getElementById("12");
```

We also know that `element`'s type will be the return type of `document.getElementById`, which we can confirm by hovering:

```typescript
// hovering over element shows:
const element: HTMLElement | null;
```

Hovering for information like this is a great way to understand what's going on, even if there isn't an error.

If we hover over `document`, we can see that it is of type `Document`. We also get a handy link to the MDN reference:

```typescript
// hovering over document shows:
var document: Document
MDN reference
```

By using hovers effectively, you can quickly understand and fix errors in your code without having to read lengthy error messages.


By using hovers effectively, you can quickly understand and fix errors in your code without having to read lengthy error messages.

Fixing Errors with Hovering

Hovering Over a Function Call

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Set up Node.js and VS Code

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Installing pnpm for Package Management

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Troubleshoot an unexpected token error in the browser when trying to import a TypeScript file.

Browsers are only able to understand JavaScript syntax, so we need to convert TypeScript syntax to JavaScript syntax for browser execution.

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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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Compiling TypeScript Files to a Directory

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Use Vite for a Frontend App with TypeScript

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Comparing Vite with tsc

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Quickly Create Scripts with tsx

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Annotating Empty Parameters

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Add a Default Parameter with `=`

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The ({ }) Syntax is used for objects in TypeScript so, this doesn't need to be shown.

Annotating with {}

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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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Function Types for Type Aliases in TypeScript

Function Types

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The `void` Type

Typing an Event Listener

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TSDoc Comments

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The Control + Space Shortcut

Manually Triggering Autocomplete

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Quick Renaming in VS Code

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The Organize Imports Hotkey in VS Code

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Refactoring with Quick Fixes

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Automatic Code Formatting with Prettier

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Introducing Union Types in TypeScript

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Literal types are assignable based on their literal values.

Literal Type Assignability

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Hovering Over a Function Call

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