Object entries in Javascript - Time & Space Complexity

Time Complexity: Object entries

O(n)

Understanding Time Complexity

We want to understand how long it takes to get all key-value pairs from an object using Object.entries.

How does the time grow when the object has more properties?

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

const obj = { a: 1, b: 2, c: 3 };
const entries = Object.entries(obj);
for (const [key, value] of entries) {
  console.log(key, value);
}
    

This code gets all key-value pairs from an object and prints them one by one.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: Looping through all entries of the object.
• How many times: Once for each property in the object.

How Execution Grows With Input

As the number of properties grows, the time to get and loop through entries grows proportionally.

Input Size (n)	Approx. Operations
10	About 10 operations
100	About 100 operations
1000	About 1000 operations

Pattern observation: The work grows in a straight line with the number of properties.

Final Time Complexity

Time Complexity: O(n)

This means the time to get all entries grows directly with the number of properties.

Common Mistake

[X] Wrong: "Object.entries is instant no matter how big the object is."

[OK] Correct: Actually, it must look at every property to make the list, so bigger objects take more time.

Interview Connect

Knowing how Object.entries works helps you explain performance when working with objects in real projects.

Self-Check

"What if we used Object.keys instead of Object.entries? How would the time complexity change?"