Iterating over
Objects in JavaScript

Introduction

In JavaScript, objects are used to store key-value pairs. Often, you'll need to loop through each key or value in an object — for example, to display user data, update values, or filter based on certain criteria.

JavaScript provides several methods to iterate over objects:

• for...in loop
• Object.keys()
• Object.values()
• Object.entries()

Example 1: Using for...in loop

The for...in loop iterates over all enumerable properties of an object.

const user = {
  name: "Alice",
  age: 30,
  city: "New York"
};

for (let key in user) {
  console.log(key + ": " + user[key]);
}
    

Output:

name: Alice
age: 30
city: New York
    

Question: What does key represent in the loop?

Answer: It represents each property name (i.e., the keys) of the object.

Example 2: Using Object.keys()

Object.keys(obj) returns an array of the object’s own enumerable property names (keys). You can use this with forEach().

const user = {
  name: "Alice",
  age: 30,
  city: "New York"
};

Object.keys(user).forEach(function(key) {
  console.log(key + ": " + user[key]);
});
    

Output:

name: Alice
age: 30
city: New York
    

This approach is clean and more functional compared to for...in.

Example 3: Using Object.values()

Object.values(obj) returns an array of the object’s values.

const user = {
  name: "Alice",
  age: 30,
  city: "New York"
};

Object.values(user).forEach(function(value) {
  console.log(value);
});
    

Output:

Alice
30
New York
    

Question: When should you use Object.values()?

Answer: When you are only interested in the values and not the keys.

Example 4: Using Object.entries()

Object.entries(obj) returns an array of key-value pairs in the format [key, value].

const user = {
  name: "Alice",
  age: 30,
  city: "New York"
};

Object.entries(user).forEach(function([key, value]) {
  console.log(key + " => " + value);
});
    

Output:

name => Alice
age => 30
city => New York
    

This is the most powerful method when you need both keys and values together in a clean, iterable format.

Comparison Table

Method	Returns	Best Use Case
for...in	Each key (including inherited enumerable)	Simple loops over keys
Object.keys()	Array of own keys	Working only with own keys
Object.values()	Array of values	Only values needed
Object.entries()	Array of [key, value] pairs	Need both keys and values

Conclusion

JavaScript offers multiple ways to iterate over object properties. The right method depends on whether you need keys, values, or both. Using modern methods like Object.entries() makes your code cleaner and more readable, especially when working with real-world data.