Object entries in Javascript - Mini Project: Build & Apply

Object entries

📖 Scenario: You have a small online store. You keep a list of products and their prices in an object.You want to see each product with its price printed out clearly.

🎯 Goal: Build a program that uses Object.entries() to get product names and prices, then prints each product with its price.

📋 What You'll Learn

Create an object called products with exact entries: 'apple': 1.2, 'banana': 0.5, 'orange': 0.8

Create a variable called entries that stores Object.entries(products)

Use a for loop with variables product and price to iterate over entries

Print each product and price in the format: Product: apple, Price: 1.2

💡 Why This Matters

🌍 Real World

Objects are used to store related data like product lists, user info, or settings in many programs.

💼 Career

Understanding how to work with objects and their entries is essential for web development and JavaScript programming jobs.

1

Create the products object

Create an object called products with these exact entries: 'apple': 1.2, 'banana': 0.5, 'orange': 0.8

Javascript

// Your code here

Hint

Use curly braces {} to create an object and separate entries with commas.

2

Get entries from the products object

Create a variable called entries that stores Object.entries(products)

Javascript

const products = { 'apple': 1.2, 'banana': 0.5, 'orange': 0.8 };
// Your code here

Hint

Use Object.entries() to get an array of key-value pairs from the object.

3

Loop over the entries

Use a for loop with variables product and price to iterate over entries

Javascript

const products = { 'apple': 1.2, 'banana': 0.5, 'orange': 0.8 };
const entries = Object.entries(products);
// Your code here

Hint

Use for (const [product, price] of entries) to get each product and price.

4

Print each product and price

Inside the loop, print each product and price in the format: Product: apple, Price: 1.2

Javascript

const products = { 'apple': 1.2, 'banana': 0.5, 'orange': 0.8 };
const entries = Object.entries(products);
for (const [product, price] of entries) {
    // Your code here
}

Hint

Use console.log with a template string to print the product and price.

Practice

1. What does Object.entries(obj) return when used on an object obj?

easy

A. A new object with the same keys and values

B. An array of values only

C. An array of keys only

D. An array of [key, value] pairs from the object

Solution

1. Step 1: Understand Object.entries behavior

   Object.entries takes an object and returns an array where each element is a two-item array: the key and its corresponding value.

2. Step 2: Compare options to definition

   Only An array of [key, value] pairs from the object correctly describes this output as an array of [key, value] pairs. Options A, C, and D describe different outputs.

3. Final Answer:

   An array of [key, value] pairs from the object -> Option D

4. Quick Check:

   Object.entries = array of [key, value] pairs [OK]

Hint: Remember: entries give key-value pairs as arrays [OK]

Common Mistakes:

• Thinking it returns an object
• Confusing entries with keys or values only
• Expecting a flat array instead of pairs

2. Which of the following is the correct syntax to get entries from an object data?

easy

A. entries(Object.data)

B. Object.entries(data)

C. Object.entry(data)

D. data.entries()

Solution

1. Step 1: Recall the correct method name and usage

   The correct method is Object.entries() called with the object as argument.

2. Step 2: Check each option

   Object.entries(data) uses the correct syntax. data.entries() is invalid because objects don't have an entries() method. Object.entry(data) uses a wrong method name. entries(Object.data) has incorrect syntax.

3. Final Answer:

   Object.entries(data) -> Option B

4. Quick Check:

   Correct method is Object.entries(obj) [OK]

Hint: Use Object.entries(obj), not obj.entries() [OK]

Common Mistakes:

• Calling entries as a method on the object
• Misspelling 'entries' as 'entry'
• Passing object incorrectly

3. What is the output of this code?

const obj = {a: 1, b: 2};
console.log(Object.entries(obj));

medium

A. ['a', 'b']

B. [['1', 'a'], ['2', 'b']]

C. [['a', 1], ['b', 2]]

D. [1, 2]

Solution

1. Step 1: Apply Object.entries to the object

   Object.entries returns an array of arrays, each inner array has the key and value from the object.

2. Step 2: Match output to options

   For obj = {a:1, b:2}, output is [['a', 1], ['b', 2]] which matches [['a', 1], ['b', 2]] exactly.

3. Final Answer:

   [['a', 1], ['b', 2]] -> Option C

4. Quick Check:

   Object.entries(obj) = [['a', 1], ['b', 2]] [OK]

Hint: Entries output is array of [key, value] pairs [OK]

Common Mistakes:

• Swapping keys and values
• Expecting a flat array of keys or values
• Confusing output format with JSON string

4. Find the error in this code snippet:

const user = {name: 'Alice', age: 25};
for (const [key, value] of user.entries()) {
  console.log(key, value);
}

medium

A. user.entries() is not a function

B. Missing curly braces in for loop

C. Destructuring syntax is incorrect

D. Console.log syntax error

Solution

1. Step 1: Identify method usage on object

   Plain objects do not have an entries() method; Object.entries() is a static method on Object.

2. Step 2: Correct usage

   To iterate entries, use for (const [key, value] of Object.entries(user)) instead of user.entries().

3. Final Answer:

   user.entries() is not a function -> Option A

4. Quick Check:

   Objects lack entries() method; use Object.entries(obj) [OK]

Hint: Use Object.entries(obj), not obj.entries() [OK]

Common Mistakes:

• Calling entries() directly on object
• Confusing Object.entries with instance method
• Ignoring error message about missing function

5. Given const data = {x: 10, y: 0, z: null, w: 'hello'}, which code snippet correctly creates a new object with only entries having truthy values?

hard

A. Object.fromEntries(Object.entries(data).filter(([k, v]) => v))

B. Object.entries(data).filter(([k, v]) => v)

C. Object.entries(data).map(([k, v]) => v && [k, v])

D. Object.fromEntries(data.filter(([k, v]) => v))

Solution

1. Step 1: Filter entries with truthy values

   Use Object.entries(data) to get pairs, then filter pairs where value is truthy (non-zero, non-null, non-false).

2. Step 2: Convert filtered entries back to object

   Use Object.fromEntries() on filtered array to create new object with only truthy values.

3. Final Answer:

   Object.fromEntries(Object.entries(data).filter(([k, v]) => v)) -> Option A

4. Quick Check:

   Filter entries then fromEntries to object [OK]

Hint: Filter entries then use Object.fromEntries to rebuild object [OK]

Common Mistakes:

• Forgetting to convert back to object
• Using map instead of filter
• Trying to call filter on object directly