Key-Value Arrays
Object.entries returns an array of [key, value] pairs.
It is great for looping and converting objects.
JavaScript Tutorial
JavaScript Object.entries()
Object.entries returns an array of key-value pairs for an object.
It is useful for iteration, filtering, and transformations.
Why We Need It
Many object transformations are easier with entries and Object.fromEntries.
This pattern keeps object logic readable and functional.
Syntax
Object.entries(obj)
Object.fromEntries(entries)Basic Example
1. Basic entries
const user = { name: "Ava", role: "admin" };
const entries = Object.entries(user);
console.log(entries);Returns [['name','Ava'], ['role','admin']].
Real World Example
2. Loop entries
const settings = { theme: "dark", layout: "grid" };
for (const [key, value] of Object.entries(settings)) {
console.log(key, value);
}Destructure key and value in a loop.
Multiple Use Cases
Transform Objects
Combine entries with map or filter to transform objects.
Use Object.fromEntries to turn pairs back into an object.
Iteration
Use for...of to iterate entries cleanly.
Destructure [key, value] in the loop.
More Examples
3. Transform values
const prices = { a: 10, b: 20 };
const doubled = Object.fromEntries(
Object.entries(prices).map(([k, v]) => [k, v * 2])
);
console.log(doubled);Map over entries to transform an object.
4. Filter entries
const data = { a: 1, b: 0, c: 3 };
const filtered = Object.fromEntries(
Object.entries(data).filter(([, v]) => v > 0)
);
console.log(filtered);Filter object properties by value.
Comparison
Without
const result = {};
for (const key in obj) {
if (Object.hasOwn(obj, key)) {
result[key] = obj[key];
}
}With
const result = Object.fromEntries(Object.entries(obj));Common Mistakes and Fixes
Expecting ordered keys
Do not rely on property order for logic.
Forgetting fromEntries
Use Object.fromEntries to rebuild objects.
Using entries for arrays
Arrays produce index-value pairs; use array methods instead.
Interview Questions
What does Object.entries return?
An array of [key, value] pairs.
How do you rebuild an object?
Use Object.fromEntries.
Why use entries?
It simplifies object iteration and transformation.
Practice Problem
Practice: Convert an object to entries, double the values, and rebuild it.
const data = { a: 2, b: 3 };
// TODO: double values using entries
One Possible Solution
const data = { a: 2, b: 3 };
const doubled = Object.fromEntries(
Object.entries(data).map(([k, v]) => [k, v * 2])
);
console.log(doubled);Frequently Asked Questions
What does Object.entries return?
An array of [key, value] pairs.
How do I convert back to object?
Use Object.fromEntries.
Does entries include inherited properties?
No, only own enumerable properties.
Try It Yourself
Try changing values and see how entries update.