Benchmark: for-in vs Object.keys()

Script Preparation code:

var obj = {
  'a': 1,
  'b': 1,
  'c': 1,
  'd': 1,
  'e': 1,
  'f': 1,
  'g': 1
};

Tests:

for-in
for (var i=10000; i > 0; i--) { for (var key in obj) { console.log(key); } }
Object.keys forEach
for (var i=10000; i > 0; i--) { Object.keys(obj).forEach(key => console.log(key)); }
Object.keys for loop
for (var i=10000; i > 0; i--) { const keys = Object.keys(obj); for (let i = 0; i < keys.length; i++) { console.log(obj[keys[i]]); } }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
for-in
Object.keys forEach
Object.keys for loop

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: one month ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/133.0.0.0 Safari/537.36

Browser/OS: Chrome 133 on Windows

View result in a separate tab

Test name	Executions per second
for-in	6.7 Ops/sec
Object.keys forEach	5.4 Ops/sec
Object.keys for loop	6.5 Ops/sec

Autogenerated LLM Summary (model llama3.2:3b, generated 6 months ago):

LLMs can make mistakes. Check important info.

The provided benchmark compares the performance of three different approaches to iterate over an object's keys: `for-in`, `Object.keys()` with a traditional `forEach` loop, and `Object.keys()` followed by a for loop.

**For-In Loop**

This approach uses the `in` operator to iterate over the object's properties. The `for-in` loop is not designed to work directly with objects; instead, it returns an iterator that allows you to access each property name. This means that the loop variable `key` is a string containing the property name, followed by `!` and then the property value.

**Object.keys() with Traditional forEach Loop**

This approach uses the `Object.keys()` method to get an array of the object's property names. It then iterates over this array using a traditional `forEach` loop, logging each key to the console.

**Object.keys() followed by For Loop**

This approach uses `Object.keys()` to get an array of the object's property names, and then iterates over this array using a for loop, logging each value associated with the property name to the console.

Pros and Cons:

*   **For-In Loop**: Pros - It's straightforward and easy to understand. However, it can be slower due to its overhead.
    *   Cons: It returns an iterator, not an array, which makes it harder to work with.
    *   Another con is that the loop variable `key` contains both the property name and value (`!`), making it difficult to use in subsequent iterations.
*   **Object.keys() with Traditional forEach Loop**: Pros - This approach can be faster than using a for-in loop since it avoids some of its overhead. However, creating an array of keys may require additional memory.
    *   Cons: The traditional `forEach` loop is not optimized for arrays and might incur some performance overhead.
*   **Object.keys() followed by For Loop**: Pros - This approach uses the most efficient method to get the property names (an array), then iterates over it using a for loop. It avoids the overhead of a traditional `forEach` loop.
    *   Cons: Creating an array and assigning its length to a variable can be slower than just iterating directly.

Additional Considerations:

*   The use of a traditional `for` loop after calling `Object.keys()` is more efficient than using a traditional `forEach` loop because it avoids the overhead associated with creating and then iterating over an iterator (as returned by `Object.keys()`).

Other Alternatives:

*   Using a for-of loop instead of a traditional `for` loop can also be faster since it's optimized to work directly with arrays and iterators.

In terms of performance, `Object.keys()` followed by a for loop tends to perform best because it minimizes overhead. This is the recommended approach in the benchmark.

Related benchmarks:

for-in vs Object.keys() (version: 0)

Comparing performance of: for-in vs Object.keys forEach vs Object.keys for loop

Created: 4 years ago by: Registered User

Jump to the latest result

for-in

Object.keys forEach

Object.keys for loop

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 6 months ago):