Benchmark: for-in vs object.keys (break test)

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) { break; } }
Object.keys
for (var i=10000; i > 0; i--) { Object.keys(obj); }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
for-in
Object.keys

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:137.0) Gecko/20100101 Firefox/137.0

Browser/OS: Firefox 137 on Ubuntu

View result in a separate tab

Test name	Executions per second
for-in	10562.4 Ops/sec
Object.keys	3046.2 Ops/sec

Autogenerated LLM Summary (model llama3.2:3b, generated one year ago):

LLMs can make mistakes. Check important info.

The provided JSON represents two JavaScript microbenchmarks, each testing the performance of different approaches for iterating over an object.

**Benchmark Comparison**

The benchmarks compare the performance of using the `for...in` loop versus the `Object.keys()` method to iterate over an object.

*   **For-in Loop**: The first benchmark uses a traditional `for...in` loop with a break statement. This approach iterates over each property in the object and breaks out as soon as it encounters the desired key (`'c'`). However, since there are multiple keys with the same value (all '1'), this approach may not be optimized for performance.
*   **Object.keys()**: The second benchmark uses the `Object.keys()` method to iterate over an array of property names in the object. This approach is generally faster than using a `for...in` loop because it avoids iterating over the entire prototype chain, which can include unnecessary properties.

**Pros and Cons**

*   **For-in Loop**:
    *   Pros: Simple and straightforward implementation.
    *   Cons: May not be optimized for performance due to potential iteration over the entire prototype chain.
    *   This approach is generally discouraged in modern JavaScript development as it's considered less efficient than other methods.
*   **Object.keys()**: 
    *   Pros: Faster execution times, especially when dealing with large objects or arrays. It also avoids iterating over the entire prototype chain, which can include unnecessary properties.
    *   Cons: May not be suitable for every use case since it returns an array of property names rather than individual values.

**Library Use**

There is no library explicitly mentioned in the provided JSON. However, both `Object.keys()` and the `for...in` loop rely on built-in JavaScript functionality.

**Special JS Features or Syntax**

Neither benchmark utilizes any special JavaScript features or syntax beyond basic object iteration methods.

**Alternative Approaches**

For iterating over an object, other approaches include:

1.  **Using Array.prototype.forEach()**: This method provides a more modern and efficient way to iterate over objects in arrays.
2.  **Using Array.prototype.entries() and a for...of loop**: Similar to `Object.keys()`, this approach returns an iterator that yields key-value pairs from the object, allowing for more control over iteration.
3.  **Using a simple for loop with array indices**: This method is straightforward but may be slower than using built-in methods like `Object.keys()` or `Array.prototype.forEach()`.
4.  **Using reduce() and map() methods**: While not directly iterating over an object, these methods can provide efficient ways to process objects in a functional programming style.

Keep in mind that the choice of iteration method depends on the specific requirements and constraints of your application.

Related benchmarks:

for-in vs object.keys (break test) (version: 0)

Comparing performance of: for-in vs Object.keys

Created: 5 years ago by: Guest

Jump to the latest result

for-in

Object.keys

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated one year ago):