Benchmark: for-in vs for-of 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
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:

No previous run results

This benchmark does not have any results yet. Be the first one to run it!

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

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark and explain what's being tested.

**Benchmark Purpose:**
The benchmark is designed to compare the performance of two approaches for iterating over an object's keys in JavaScript:

1. `for...in` loop
2. Using `Object.keys()` function

**Options Compared:**

* `for-in`: This approach uses a traditional `for...in` loop to iterate over the object's properties (keys). The loop iterates over the property names and their values, allowing you to access both under the same iteration.
* `Object.keys()`: This approach uses the `Object.keys()` function to retrieve an array of a given object's own enumerable property names. It then iterates over this array using a traditional `for...of` loop.

**Pros and Cons:**

* `for-in`:
	+ Pros:
		- Can access both properties (key-value pairs) under the same iteration.
		- Can be used for objects that need to iterate over their own properties, like in certain DOM manipulation scenarios.
	+ Cons:
		- Does not provide any guarantees about the order of property iteration. In older browsers, `for-in` may yield an arbitrary order.
		- Can lead to slower performance due to the overhead of checking if a property is enumerable.
* `Object.keys()`:
	+ Pros:
		- Provides predictable and consistent ordering of property iteration across all modern browsers.
		- Does not require any additional processing or checks, making it faster than `for-in`.
	+ Cons:
		- Only yields the property names (keys) without their values. If you need to access both, this approach requires additional iteration.

**Library/Function Used:**
In neither of these test cases is a specific library used beyond what's built into JavaScript. However, it's worth noting that `Object.keys()` was introduced in ECMAScript 2015 (ES6) as part of the standard language specification.

**Special JS Feature/Syntax:**
None are specifically mentioned or required for these benchmark tests.

**Other Alternatives:**
If you need to iterate over an object's properties, other alternatives might include:

* Using a `for...of` loop with an iterator (e.g., `Object.entries()` or `Object.keys()`)
* Utilizing modern array methods like `forEach()`
* Using libraries like Lodash, which provides an `keys()` function for iterating over object keys

Keep in mind that these alternatives might not provide the exact same performance characteristics as the original `for-in` and `Object.keys()` approaches.

Related benchmarks:

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

Comparing performance of: for-in vs Object.keys

Created: 4 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

No previous run results

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