JS Object Keys, Values, and Entries Full Guide

Master Object.keys(), Object.values(), and Object.entries() in JavaScript. Learn how to iterate over objects, transform data, filter properties, and convert between objects and arrays with practical examples.

JavaScriptbeginner

RuneHub Team

February 28, 2026

14 min read

RuneHub Team

Feb 28, 2026

14 min read

JavaScript objects do not have built-in array methods like map, filter, or reduce. To iterate over and transform object data, you first need to convert the object into an array using Object.keys(), Object.values(), or Object.entries(). These three methods are among the most frequently used tools in JavaScript development, powering everything from data transformation to UI rendering.

This guide covers all three methods with practical examples, shows how to combine them with array methods, and teaches common patterns for working with object data.

Object.keys()

Object.keys() returns an array of an object's own enumerable string property names:

javascript

const user = {
  name: "Alice",
  age: 28,
  email: "alice@example.com",
  role: "developer"
};
 
const keys = Object.keys(user);
console.log(keys);
// ["name", "age", "email", "role"]

Counting Properties

javascript

const product = {
  name: "Laptop",
  price: 999,
  brand: "TechBrand",
  inStock: true
};
 
console.log(Object.keys(product).length); // 4

Checking for Empty Objects

javascript

function isEmpty(obj) {
  return Object.keys(obj).length === 0;
}
 
console.log(isEmpty({}));           // true
console.log(isEmpty({ a: 1 }));    // false
console.log(isEmpty(new Object())); // true

Iterating with Object.keys

javascript

const scores = {
  math: 92,
  science: 88,
  english: 95,
  history: 78
};
 
Object.keys(scores).forEach(subject => {
  console.log(`${subject}: ${scores[subject]}`);
});
// math: 92
// science: 88
// english: 95
// history: 78

Object.values()

Object.values() returns an array of an object's own enumerable property values:

javascript

const user = {
  name: "Alice",
  age: 28,
  email: "alice@example.com"
};
 
const values = Object.values(user);
console.log(values);
// ["Alice", 28, "alice@example.com"]

Calculating with Values

javascript

const monthlyExpenses = {
  rent: 1500,
  food: 400,
  transport: 120,
  utilities: 200,
  entertainment: 150
};
 
// Sum all values
const total = Object.values(monthlyExpenses).reduce((sum, cost) => sum + cost, 0);
console.log(`Total: $${total}`); // "Total: $2370"
 
// Find highest expense
const highest = Math.max(...Object.values(monthlyExpenses));
console.log(`Highest: $${highest}`); // "Highest: $1500"
 
// Average expense
const avg = total / Object.values(monthlyExpenses).length;
console.log(`Average: $${avg.toFixed(2)}`); // "Average: $474.00"

Checking if a Value Exists

javascript

const permissions = {
  read: true,
  write: true,
  delete: false,
  admin: false
};
 
const hasAnyEnabled = Object.values(permissions).some(v => v === true);
console.log(hasAnyEnabled); // true
 
const allEnabled = Object.values(permissions).every(v => v === true);
console.log(allEnabled); // false

Object.entries()

Object.entries() returns an array of [key, value] pairs, which is the most versatile of the three methods:

javascript

const user = {
  name: "Alice",
  age: 28,
  role: "developer"
};
 
const entries = Object.entries(user);
console.log(entries);
// [["name", "Alice"], ["age", 28], ["role", "developer"]]

Iterating with Destructuring

Object.entries pairs perfectly with destructuring in loops:

javascript

const inventory = {
  laptops: 45,
  phones: 120,
  tablets: 30,
  monitors: 65
};
 
for (const [product, count] of Object.entries(inventory)) {
  console.log(`${product}: ${count} units`);
}
// laptops: 45 units
// phones: 120 units
// tablets: 30 units
// monitors: 65 units

Filtering Object Properties

javascript

const scores = {
  Alice: 92,
  Bob: 65,
  Charlie: 88,
  Diana: 45,
  Eve: 97
};
 
// Keep only passing scores (>= 70)
const passing = Object.fromEntries(
  Object.entries(scores).filter(([name, score]) => score >= 70)
);
 
console.log(passing);
// { Alice: 92, Charlie: 88, Eve: 97 }

Transforming Object Data

javascript

const prices = {
  apple: 1.50,
  banana: 0.75,
  orange: 2.00,
  mango: 3.50
};
 
// Apply 20% discount to all prices
const discounted = Object.fromEntries(
  Object.entries(prices).map(([fruit, price]) => [fruit, +(price * 0.8).toFixed(2)])
);
 
console.log(discounted);
// { apple: 1.2, banana: 0.6, orange: 1.6, mango: 2.8 }

Comparison of All Three Methods

Method	Returns	Best For
`Object.keys(obj)`	`string[]`	Counting properties, checking existence, key-based iteration
`Object.values(obj)`	`any[]`	Calculations, aggregations, value-based checks
`Object.entries(obj)`	`[string, any][]`	Full iteration, transformation, filtering, conversion

javascript

const product = {
  name: "Laptop",
  price: 999,
  inStock: true
};
 
console.log(Object.keys(product));    // ["name", "price", "inStock"]
console.log(Object.values(product));  // ["Laptop", 999, true]
console.log(Object.entries(product)); // [["name", "Laptop"], ["price", 999], ["inStock", true]]

Object.fromEntries()

Object.fromEntries() is the reverse of Object.entries(). It converts an array of [key, value] pairs back into an object:

javascript

const entries = [
  ["name", "Alice"],
  ["age", 28],
  ["role", "developer"]
];
 
const user = Object.fromEntries(entries);
console.log(user);
// { name: "Alice", age: 28, role: "developer" }

Converting Map to Object

javascript

const userMap = new Map([
  ["name", "Alice"],
  ["age", 28],
  ["email", "alice@example.com"]
]);
 
const userObj = Object.fromEntries(userMap);
console.log(userObj);
// { name: "Alice", age: 28, email: "alice@example.com" }

entries + fromEntries Pipeline

The entries → transform → fromEntries pipeline is the standard pattern for transforming objects:

javascript

const rawData = {
  "  Name  ": "  Alice  ",
  " Email": " alice@example.com ",
  "Role  ": "  developer "
};
 
// Clean up all keys and values
const cleaned = Object.fromEntries(
  Object.entries(rawData).map(([key, value]) => [
    key.trim().toLowerCase(),
    typeof value === "string" ? value.trim() : value
  ])
);
 
console.log(cleaned);
// { name: "Alice", email: "alice@example.com", role: "developer" }

Practical Patterns

Grouping Array Items into an Object

javascript

const orders = [
  { id: 1, category: "electronics", total: 299 },
  { id: 2, category: "clothing", total: 49 },
  { id: 3, category: "electronics", total: 599 },
  { id: 4, category: "food", total: 25 },
  { id: 5, category: "clothing", total: 89 }
];
 
const grouped = orders.reduce((acc, order) => {
  const key = order.category;
  if (!acc[key]) acc[key] = [];
  acc[key].push(order);
  return acc;
}, {});
 
// Summary per category
const summary = Object.fromEntries(
  Object.entries(grouped).map(([category, items]) => [
    category,
    {
      count: items.length,
      total: items.reduce((sum, o) => sum + o.total, 0)
    }
  ])
);
 
console.log(summary);
// { electronics: { count: 2, total: 898 }, clothing: { count: 2, total: 138 }, food: { count: 1, total: 25 } }

Inverting an Object (Swap Keys and Values)

javascript

const statusCodes = {
  200: "OK",
  404: "Not Found",
  500: "Internal Server Error",
  403: "Forbidden"
};
 
const statusNames = Object.fromEntries(
  Object.entries(statusCodes).map(([code, name]) => [name, Number(code)])
);
 
console.log(statusNames);
// { OK: 200, "Not Found": 404, "Internal Server Error": 500, Forbidden: 403 }

Picking Specific Properties

javascript

function pick(obj, keys) {
  return Object.fromEntries(
    Object.entries(obj).filter(([key]) => keys.includes(key))
  );
}
 
function omit(obj, keys) {
  return Object.fromEntries(
    Object.entries(obj).filter(([key]) => !keys.includes(key))
  );
}
 
const user = {
  id: 42,
  name: "Alice",
  email: "alice@example.com",
  password: "secret",
  role: "admin"
};
 
console.log(pick(user, ["name", "email"]));
// { name: "Alice", email: "alice@example.com" }
 
console.log(omit(user, ["password", "role"]));
// { id: 42, name: "Alice", email: "alice@example.com" }

Sorting an Object by Values

javascript

const scores = {
  Alice: 92,
  Bob: 65,
  Charlie: 88,
  Diana: 97,
  Eve: 78
};
 
const sorted = Object.fromEntries(
  Object.entries(scores).sort(([, a], [, b]) => b - a)
);
 
console.log(sorted);
// { Diana: 97, Alice: 92, Charlie: 88, Eve: 78, Bob: 65 }

Property Order

Objects in JavaScript maintain insertion order for string keys (with numeric-like keys sorted first):

javascript

const mixed = { b: 2, a: 1, "2": "two", "1": "one", c: 3 };
 
console.log(Object.keys(mixed));
// ["1", "2", "b", "a", "c"]
// Numeric keys come first (sorted), then string keys in insertion order

Best Practices

Use Object.entries as your default when you need both keys and values
Combine with array methods: entries → map/filter/reduce → fromEntries is the standard transformation pipeline
Prefer Object.keys().length over for...in loops for counting properties
Use destructuring in entries callbacks: ([key, value]) => instead of (entry) => entry[0]
Use Object.fromEntries() to convert transformed entries back to objects cleanly

Common Mistakes to Avoid

Modifying Objects During Iteration

javascript

const data = { a: 1, b: 2, c: 3 };
 
// WRONG: modifying while iterating (unpredictable)
for (const key of Object.keys(data)) {
  if (data[key] < 2) delete data[key]; // Risky!
}
 
// CORRECT: create a new object with filter
const filtered = Object.fromEntries(
  Object.entries(data).filter(([, value]) => value >= 2)
);
console.log(filtered); // { b: 2, c: 3 }

Forgetting Object.keys Returns Strings

javascript

const data = { 1: "one", 2: "two", 3: "three" };
 
Object.keys(data).forEach(key => {
  console.log(typeof key); // "string" (not number!)
  console.log(key === 1);  // false (string !== number)
  console.log(key === "1"); // true
});

Rune AI

Key Insights

Object.keys(): Returns an array of property names; ideal for counting, existence checks, and key iteration
Object.values(): Returns an array of property values; perfect for calculations and aggregations
Object.entries(): Returns [key, value] pairs; the most versatile for full transformation pipelines
Object.fromEntries(): Converts entries back to objects, completing the entries → transform → fromEntries workflow
Own enumerable only: All three methods skip inherited and non-enumerable properties, making them safer than for...in

Frequently Asked Questions

Do these methods include inherited properties?

No. All three methods (`Object.keys`, `Object.values`, `Object.entries`) return only the object's **own** enumerable properties. Properties inherited from the prototype chain are excluded. This is one reason they are preferred over `for...in` [loops](/tutorials/programming-languages/javascript/javascript-loops-tutorial-for-while-do-while), which do iterate over inherited properties.

Do they include Symbol properties?

No. These methods only return string-keyed properties. To get Symbol properties, use `Object.getOwnPropertySymbols(obj)`. To get all own properties (both strings and symbols), use `Reflect.ownKeys(obj)`.

What is the difference between Object.keys and for...in?

`Object.keys()` returns an array of own enumerable string keys. A `for...in` loop iterates over own AND inherited enumerable string keys. `Object.keys` is generally preferred because it avoids prototype chain surprises and returns an array you can chain with [map](/tutorials/programming-languages/javascript/how-to-use-the-javascript-array-map-method-today), [filter](/tutorials/programming-languages/javascript/javascript-array-filter-method-complete-tutorial), and reduce.

Can I use these on arrays?

Yes, since arrays are objects. `Object.keys([10, 20, 30])` returns `["0", "1", "2"]` (string indices), and `Object.values([10, 20, 30])` returns `[10, 20, 30]`. However, regular array methods are more appropriate for working with arrays.

Is the property order guaranteed?

Since ES2015, JavaScript engines maintain a deterministic property order: integer-like keys first (sorted numerically), then string keys in insertion order, then symbols in insertion order. `Object.keys`, `Object.values`, and `Object.entries` all follow this order.

Conclusion

Object.keys(), Object.values(), and Object.entries() bridge the gap between objects and arrays in JavaScript. They convert object data into arrays that you can iterate, transform, filter, and reduce using the full power of array methods. Combined with Object.fromEntries(), they form a complete pipeline for object data transformation. Mastering these four methods unlocks clean, functional patterns for working with any object-shaped data in your applications.

JS Object Keys, Values, and Entries Full Guide

Object.keys()

Counting Properties

Checking for Empty Objects

Iterating with Object.keys

Object.values()

Calculating with Values

Checking if a Value Exists

Object.entries()

Iterating with Destructuring

Filtering Object Properties

Transforming Object Data

Comparison of All Three Methods

Object.fromEntries()

Converting Map to Object

entries + fromEntries Pipeline

Practical Patterns

Grouping Array Items into an Object

Inverting an Object (Swap Keys and Values)

Picking Specific Properties

Sorting an Object by Values

Property Order

Best Practices

Common Mistakes to Avoid

Modifying Objects During Iteration

Forgetting Object.keys Returns Strings

Rune AI

Frequently Asked Questions

Do these methods include inherited properties?

Do they include Symbol properties?

What is the difference between Object.keys and for...in?

Can I use these on arrays?

Is the property order guaranteed?

Conclusion

Tags

More in this topic

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Advanced Web Workers for High Performance JS

JavaScript Macros and Abstract Code Generation

JS Object Keys, Values, and Entries Full Guide

Object.keys()

Counting Properties

Checking for Empty Objects

Iterating with Object.keys

Object.values()

Calculating with Values

Checking if a Value Exists

Object.entries()

Iterating with Destructuring

Filtering Object Properties

Transforming Object Data

Comparison of All Three Methods

Object.fromEntries()

Converting Map to Object

entries + fromEntries Pipeline

Practical Patterns

Grouping Array Items into an Object

Inverting an Object (Swap Keys and Values)

Picking Specific Properties

Sorting an Object by Values

Property Order

Best Practices

Common Mistakes to Avoid

Modifying Objects During Iteration

Forgetting Object.keys Returns Strings

Rune AI

Frequently Asked Questions

Do these methods include inherited properties?

Do they include Symbol properties?

What is the difference between Object.keys and for...in?

Can I use these on arrays?

Is the property order guaranteed?

Conclusion

Tags

More in this topic

OffscreenCanvas API in JS for UI Performance

Advanced Web Workers for High Performance JS

JavaScript Macros and Abstract Code Generation