Week 6 - Advanced topics

Synchronous File IO

File processing

Error handling

Array methods

Closures

Style - How to write meaningful comments

Practice

Assignment

• Teachers

Core program

Content

Let’s get practical

Exercise 1: Contact Book (File I/O)

Build a simple contact management system using files.

Requirements:

1. Create functions to manage contacts.txt:
   • addContact(name, phone) - append contact in format "Name: Phone"
   • listContacts() - read and display all contacts
   • searchContact(name) - find and return matching contact
2. Test by adding 5 contacts, listing them, and searching for one
3. Handle case where file doesn't exist (create it)

Challenge: Create deleteContact(name) that removes a contact and rewrites the file.

Exercise 2: Safe JSON Config (Error Handling)

Write robust configuration file handling with proper error management.

Requirements:

1. Create loadConfig(filename) that:
   • Reads JSON config file
   • Returns parsed object
   • If file missing: creates default {theme: 'light', notifications: true}
   • If invalid JSON: backs up corrupted file as .corrupted and creates new default
   • If other error: throws with helpful message
2. Create saveConfig(filename, config) with error handling
3. Test with: missing file, corrupted JSON, and valid file

Challenge: Add validation that throws errors for invalid config values before saving.

Exercise 3: Product Filter Pipeline (Array Methods)

Process product data using chained array methods.

Requirements:

1. Start with array of 10 products: {name, price, category, rating, inStock}
2. Chain methods to:
   • Filter in-stock items
   • Filter items with rating > 4
   • Sort by price (low to high)
   • Map to create {name, price} objects only
   • Get first 3 results with slice()
3. Calculate average price of filtered products using reduce()

Bonus: Use every() to check if all remaining products are under €100.

Exercise 4: Student Grade Analysis (Array Methods)

Analyze student performance data.

Requirements:

1. Create array of students: {name, grades: [85, 92, 78, ...]}
2. Use map() to add average property to each student
3. Use filter() to find students with average > 80
4. Use find() to locate student with highest average
5. Use some() to check if any student failed (average < 60)
6. Use reduce() to calculate class average

Challenge: Sort students by average and use forEach() to print rankings.

Exercise 5: Array Method Mastery (Array Methods)

Practice all array methods with a single dataset.

Requirements:

1. Start with: [12, 5, 8, 130, 44, 3, 88, 22]
2. Use filter() to get numbers > 10
3. Use map() to double each number
4. Use sort() to order ascending
5. Use find() to get first number > 100
6. Use every() to check if all are positive
7. Use reduce() to sum all numbers

Challenge: Create your own array and apply at least 5 different methods in a meaningful chain.

Exercise 6: Private Counter Factory (Closures)

Build counter objects with private state using closures.

Requirements:

1. Create createCounter(start, step) that returns object with:
   • increment() - increases by step
   • decrement() - decreases by step
   • getValue() - returns current value
   • reset() - returns to start value
2. The count variable must be private (not accessible outside)
3. Create 3 different counters with different configurations
4. Demonstrate they maintain independent state

Challenge: Add getHistory() that returns array of all values the counter has had (use closure to track).

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