codex-lv2-may-2025

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Current Level: 2

Lesson: What is a POJO? — 4 Exercises

🎯 Objective

Learn to identify keys and values, create your own POJOs, explain object representations, and fix syntax errors.

📚 Key Terms Explained

Before we dive into the exercises, let’s understand the important terms we’ll be using:

Property

A property is a piece of information stored in an object. Think of it like a characteristic or attribute of something.

Example:

const car = {
    "make": "Toyota",    // This is a property
    "model": "Corolla",  // This is a property
    "year": 2020         // This is a property
};

Key

A key is the name of a property. It’s like a label that tells us what information we’re storing.

Example:

const pet = {
    "name": "Buddy",     // "name" is the key
    "species": "Dog",    // "species" is the key
    "age": 5            // "age" is the key
};

Value

A value is the actual data stored in a property. It can be a string, number, boolean, or other data type.

Example:

const book = {
    "title": "JavaScript for Beginners",  // "JavaScript for Beginners" is the value
    "author": "Jane Doe",                 // "Jane Doe" is the value
    "pages": 250,                        // 250 is the value
    "isPublished": true                  // true is the value
};

Key-Value Pairs

Together, a key and its value form a key-value pair:

"key": "value"

In the example above:

"title" is the key
"JavaScript for Beginners" is the value
Together they form the key-value pair: "title": "JavaScript for Beginners"

✅ Example (Completed for You)

This is a completed example of a POJO with comments explaining each part.

const car = {
    "make": "Toyota",
    "model": "Corolla",
    "year": 2020
};

console.log(car.make);    // Prints: Toyota
console.log(car.model);   // Prints: Corolla
console.log(car.year);    // Prints: 2020

// Now let's update the year
car.year = 2024;

console.log(car.year);    // Prints: 2024

// Summary comment:
// - car is a POJO with three properties: make, model, year.
// - We used dot notation to read the properties.
// - We updated the year from 2020 to 2024.

✅ Exercise 1: Identify Keys and Values

const book = {
    "title": "JavaScript for Beginners",
    "author": "Jane Doe",
    "pages": 250,
    "isPublished": true
};

// TODO: List all the keys as a comment
// TODO: List all the values as a comment

✅ Exercise 2: Create Your Own POJO

const pet = {
    "name": "Buddy",
    "species": "Dog",
    "age": 5
};

console.log(pet);

// TODO: What are the values for name, species, and age? Write as comments.

✅ Exercise 3: Explain This POJO

const sprite = {
    "name": "Hero",
    "x": 100,
    "y": 200
};

console.log(sprite);

// TODO: What does this object represent? Write your explanation as a comment.

✅ Exercise 4: Fix the Syntax

const car = {
    "make": "Toyota",
    "model": "Corolla",
    "year": 2020
    "color": "Blue"
};

// TODO: Fix the syntax error.
// TODO: Explain what was wrong in a comment.
console.log(car);

✅ ACP after completing the exercises

git add script.js
git commit -m "Step 2 - Exercises completed"
git push

✅ Summary

You learned:

How to identify keys and values in a POJO.
How to create and describe POJOs.
How to fix syntax errors in object definitions.

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Current Level: 2