Monaco Editor in Slidev

This skill covers integrating Monaco Editor (the editor powering VS Code) into your Slidev presentations for live coding, interactive demos, and executable code blocks.

When to Use This Skill

Live coding demonstrations
Interactive code editing during presentations
Running code examples in real-time
Teaching programming concepts
Showing auto-completion and type hints

Enabling Monaco Editor

Basic Monaco Block

Add {monaco} to any code block:

```typescript {monaco}
const greeting = 'Hello, World!'
console.log(greeting)
```

This creates an editable code block with:

Syntax highlighting
Auto-completion
Type checking (for TypeScript)
Bracket matching

Monaco with Line Highlighting

```typescript {monaco}{2,3}
const a = 1
const b = 2  // highlighted
const c = 3  // highlighted
```

Monaco Runner

Execute code directly in the presentation:

JavaScript Runner

```javascript {monaco-run}
const numbers = [1, 2, 3, 4, 5]
const doubled = numbers.map(n => n * 2)
console.log(doubled)
```

Click "Run" to execute and see output.

TypeScript Runner

```typescript {monaco-run}
interface User {
  name: string
  age: number
}

const user: User = {
  name: 'John',
  age: 30
}

console.log(`${user.name} is ${user.age} years old`)
```

Auto-Run on Load

```javascript {monaco-run} {autorun:true}
console.log('This runs automatically!')
```

Show Output Only

```javascript {monaco-run} {showOutputAt:'+1'}
// Output shows after one click
console.log('Hello!')
```

Configuration Options

Editor Height

```typescript {monaco}{height:'300px'}
// Taller editor
function longFunction() {
  // ...
}
```

Read-Only Mode

```typescript {monaco}{readonly:true}
// Cannot be edited
const CONSTANT = 'value'
```

Diff Editor

```typescript {monaco-diff}
const original = 'Hello'
~~~
const modified = 'Hello, World!'
```

Monaco Setup Configuration

setup/monaco.ts

import { defineMonacoSetup } from '@slidev/types'

export default defineMonacoSetup((monaco) => {
  // Editor options
  return {
    editorOptions: {
      fontSize: 14,
      fontFamily: 'JetBrains Mono, monospace',
      minimap: { enabled: false },
      lineNumbers: 'on',
      wordWrap: 'on',
      tabSize: 2,
      scrollBeyondLastLine: false,
      automaticLayout: true,
    },
    // Light/dark theme
    theme: {
      light: 'vs',
      dark: 'vs-dark',
    },
  }
})

Custom Themes

import { defineMonacoSetup } from '@slidev/types'

export default defineMonacoSetup((monaco) => {
  // Define custom theme
  monaco.editor.defineTheme('my-theme', {
    base: 'vs-dark',
    inherit: true,
    rules: [
      { token: 'comment', foreground: '6A9955' },
      { token: 'keyword', foreground: 'C586C0' },
    ],
    colors: {
      'editor.background': '#1a1a2e',
    },
  })

  return {
    theme: {
      dark: 'my-theme',
      light: 'vs',
    },
  }
})

Type Definitions

Adding Types for Libraries

// setup/monaco.ts
import { defineMonacoSetup } from '@slidev/types'

export default defineMonacoSetup(async (monaco) => {
  // Add React types
  const reactTypes = await fetch(
    'https://unpkg.com/@types/react/index.d.ts'
  ).then(r => r.text())

  monaco.languages.typescript.typescriptDefaults.addExtraLib(
    reactTypes,
    'file:///node_modules/@types/react/index.d.ts'
  )
})

Inline Type Definitions

```typescript {monaco}
// Types defined inline
interface Todo {
  id: number
  text: string
  completed: boolean
}

const todos: Todo[] = [
  { id: 1, text: 'Learn Slidev', completed: true },
  { id: 2, text: 'Create presentation', completed: false },
]
```

Interactive Examples

Counter Demo

```typescript {monaco-run}
// Interactive counter
let count = 0

function increment() {
  count++
  console.log(`Count: ${count}`)
}

// Click Run multiple times!
increment()
```

API Simulation

```typescript {monaco-run}
// Simulated API call
async function fetchUser(id: number) {
  // Simulate network delay
  await new Promise(r => setTimeout(r, 500))

  return {
    id,
    name: 'John Doe',
    email: 'john@example.com'
  }
}

const user = await fetchUser(1)
console.log(user)
```

Algorithm Visualization

```typescript {monaco-run}
// Bubble sort with steps
function bubbleSort(arr: number[]) {
  const result = [...arr]
  const steps: string[] = []

  for (let i = 0; i < result.length; i++) {
    for (let j = 0; j < result.length - i - 1; j++) {
      if (result[j] > result[j + 1]) {
        [result[j], result[j + 1]] = [result[j + 1], result[j]]
        steps.push(`Swap: [${result.join(', ')}]`)
      }
    }
  }

  return { result, steps }
}

const { result, steps } = bubbleSort([5, 3, 8, 4, 2])
console.log('Steps:', steps.length)
steps.forEach(s => console.log(s))
console.log('Final:', result)
```

Code Runner Patterns

Show Concept Then Let Edit

# Array Methods

```typescript {monaco-run}
const numbers = [1, 2, 3, 4, 5]

// Try changing the function!
const result = numbers
  .filter(n => n % 2 === 0)
  .map(n => n * 2)

console.log(result)
```

Try modifying the code to:
- Filter odd numbers
- Triple instead of double

Interactive Quiz

# Fix the Bug

```typescript {monaco-run}
// This code has a bug - can you fix it?
function reverseString(str: string) {
  return str.split('').reserve().join('')
}

console.log(reverseString('hello'))
// Expected: 'olleh'
```

Live Data Manipulation

```typescript {monaco-run}
const data = [
  { name: 'Alice', score: 85 },
  { name: 'Bob', score: 92 },
  { name: 'Charlie', score: 78 },
]

// Calculate statistics
const average = data.reduce((sum, d) => sum + d.score, 0) / data.length
const highest = Math.max(...data.map(d => d.score))
const passing = data.filter(d => d.score >= 80)

console.log(`Average: ${average.toFixed(1)}`)
console.log(`Highest: ${highest}`)
console.log(`Passing: ${passing.map(d => d.name).join(', ')}`)
```

Combining with Animations

Reveal Then Edit

<v-click>

```typescript {monaco}
// Code appears on click, then is editable
function greet(name: string) {
  return `Hello, ${name}!`
}
```

</v-click>

Step-by-Step with Monaco

<v-clicks>

Start with this code:

```typescript {monaco}
const x = 1
```

Then try adding more lines!

</v-clicks>

Best Practices

1. Keep Examples Focused

```typescript {monaco-run}
// GOOD: Single concept
const sum = [1, 2, 3].reduce((a, b) => a + b, 0)
console.log(sum) // 6
```

2. Provide Starting Point

```typescript {monaco-run}
// Complete the function:
function capitalize(str: string): string {
  // Your code here
  return str
}

console.log(capitalize('hello')) // Should print: 'Hello'
```

3. Show Expected Output

```typescript {monaco-run}
// Code example
const result = [1, 2, 3].map(n => n ** 2)
console.log(result)
// Expected output: [1, 4, 9]
```

4. Handle Errors Gracefully

```typescript {monaco-run}
try {
  const result = riskyOperation()
  console.log(result)
} catch (error) {
  console.error('Error:', error.message)
}

function riskyOperation() {
  // Might throw an error
  throw new Error('Oops!')
}
```

Limitations

No DOM Access: Cannot manipulate the page DOM
Limited APIs: Only standard JavaScript APIs available
No Imports: Cannot import external packages
Console Only: Output is console-based

Output Format

When creating Monaco code blocks:

PURPOSE: [What the code demonstrates]
INTERACTION: [How audience should interact]

CODE:
```[language] {monaco-run}
// Clear comments explaining purpose

[Code with good defaults]

// Expected output noted

SUGGESTED EDITS:

Try changing X to Y
Modify function to do Z

slidev-monaco-editor