Benchmark: for-in vs for-of 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) { if (!obj.hasOwnProperty(key)) { continue } console.log(key); } }
Object.keys
for (var i=10000; i > 0; i--) { for (var key of Object.keys(obj)) { console.log(key) } }

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 (Macintosh; Intel Mac OS X 10.15; rv:131.0) Gecko/20100101 Firefox/131.0

Browser/OS: Firefox 131 on Mac OS X 10.15

View result in a separate tab

for-in

6/s

Object.keys

6/s

View exact numbers

Test name	Executions per second
✓ for-in	6 Ops/sec
Object.keys	6 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's dive into the world of JavaScript microbenchmarks on MeasureThat.net.

**Benchmark Definition**

The provided JSON represents a benchmark definition, which is a template for creating and running JavaScript microbenchmarks. The template includes:

1. `Name`: A unique name for the benchmark.
2. `Description`: An optional description of the benchmark (in this case, null).
3. `Script Preparation Code`: A code snippet that sets up the test environment and objects used in the benchmark.
4. `Html Preparation Code`: An optional HTML code snippet that can be used to create a user interface for the benchmark (in this case, null).

In this specific benchmark definition, we have two object literals with 7 properties each.

**Test Cases**

The benchmark consists of two test cases:

1. **for-in**: This test case uses an iterative approach to iterate over the `obj` object's properties.
2. **Object.keys**: This test case uses the built-in `Object.keys()` method to iterate over the `obj` object's properties.

**Comparison of Options**

The two test cases differ in their approach:

1. **for-in**: This method uses the `in` operator to check if a property exists in the object, which can lead to slower performance compared to other methods.
2. **Object.keys**: This method uses the `Object.keys()` function, which is generally faster and more efficient than using `in`.

**Pros and Cons**

Here's a summary of the pros and cons for each approach:

* **for-in**:
	+ Pros: Can be used with arrays and objects.
	+ Cons: May lead to slower performance due to property existence checks.
* **Object.keys**:
	+ Pros: Generally faster and more efficient than using `in`.
	+ Cons: Limited to iterating over object properties.

**Library Used**

In this benchmark, the built-in `Object.keys()` method is used, which is a part of the JavaScript language itself. This means that the performance difference between the two test cases is largely due to the specific implementation and optimization of the `Object.keys()` function in each browser version.

**Special JS Feature or Syntax**

There are no special features or syntaxes being tested in this benchmark. The code snippets provided are standard JavaScript code, without any experimental or proposal features.

**Other Alternatives**

If you'd like to explore alternative approaches, here are a few options:

1. **for...of**: This method uses an iterative approach similar to `Object.keys()`, but with a different syntax.
2. **forEach**: This method can be used to iterate over the object's properties, but it may not provide the same level of performance as `Object.keys()`.

Note that these alternatives might have their own trade-offs in terms of performance, readability, and browser compatibility.

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

Comparing performance of: `for-in vs Object.keys`

Created: 4 years ago by: Guest

Go 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):

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

Comparing performance of: for-in vs Object.keys

Created: 4 years ago by: Guest

Go 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):

Related benchmarks

Comparing performance of: `for-in vs Object.keys`