Benchmark: for-in vs object.keys map

Script Preparation code:

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

Tests:

for-in
const arr = []; for (var i=10000; i > 0; i--) { for (var key in obj) { arr.push(key); } }
Object.keys
for (var i=10000; i > 0; i--) { Object.keys(obj).map(key => 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: 2 years ago)

User agent: Mozilla/5.0 (iPhone; CPU iPhone OS 17_1_2 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/17.1.2 Mobile/15E148 Safari/604.1

Browser/OS: Mobile Safari 17 on iOS 17.1.2

View result in a separate tab

for-in

2K/s

Object.keys

951/s

View exact numbers

Test name	Executions per second
✓ for-in	2,369 Ops/sec
Object.keys	951 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down what's being tested in this benchmark.

**Benchmark Goal:**
The goal of this benchmark is to compare the performance of three different approaches for iterating over an object and extracting its keys:

1. Using `for...in` loop
2. Using `Object.keys()` method
3. Using `map()` function with `Object.keys()`

**Options Compared:**

* **For-in Loop**: Iterates over an object using the `for...in` loop, which iterates over the object's properties (including inherited ones) and assigns them to a variable in each iteration.
* **Object.keys() Method**: Returns an array of strings containing the property names of an object.
* **Map Function with Object.keys()**: Uses the `map()` function to apply a transformation to each key in the object, which returns an array of keys.

**Pros and Cons:**

* **For-in Loop**:
	+ Pros: Simple and intuitive, can be used for other purposes besides iterating over objects (e.g., iterating over arrays).
	+ Cons: Iterates over inherited properties, can lead to unexpected behavior if not handled carefully.
* **Object.keys() Method**:
	+ Pros: Fast and efficient, returns only the property names of the object, does not iterate over inherited properties.
	+ Cons: May not be suitable for all use cases (e.g., when using older browsers that don't support it).
* **Map Function with Object.keys()**:
	+ Pros: Can be used to perform additional transformations on each key, can be more memory-efficient than creating an array of keys.
	+ Cons: Can be slower due to the extra overhead of `map()` function.

**Library Used (if any):**
None in this case. The benchmark is testing only JavaScript core features and standard libraries.

**Special JS Feature or Syntax:**
There's no specific special feature or syntax being tested here, just standard JavaScript core features.

Now, let's talk about the benchmark preparation code:

* **Script Preparation Code**: Creates an object `obj` with 11 properties (keys) and assigns a value of 1 to each property.
* **Html Preparation Code**: None in this case. The benchmark is testing only JavaScript performance, so no HTML or CSS is involved.

**Other Alternatives:**
Some other alternatives for iterating over objects and extracting keys include:

* Using `for...of` loop (which iterates over the object's own properties)
* Using a `forEach()` function with an arrow function
* Using a library like Lodash or Ramda, which provide more functional programming style APIs for working with data structures.

Keep in mind that these alternatives may have different performance characteristics and use cases than the options being tested here.

for-in vs object.keys map (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 object.keys map (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`