Benchmark: for..in or keys+forEach

Script Preparation code:

testObj = {};
for(let i = 0; i < 1000; i++) {
  testObj['a'+i] = i;
}

Tests:

for..in
let acc = 0; for (let k in testObj) { acc += testObj[k]; }
keys+forEach
let acc = 0; Object.keys(testObj).forEach((k) => { acc += testObj[k]; });

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
for..in
keys+forEach

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 25 days ago):

LLMs can make mistakes. Check important info.

**Benchmark Overview**

MeasureThat.net is a website that allows users to create and run JavaScript microbenchmarks. The provided benchmark definition and individual test cases aim to compare the performance of two approaches: `for..in` and `keys+forEach`.

**What are being tested?**

The benchmark tests the performance of two different ways to iterate over an object's properties in JavaScript:

1. **`for..in`**: This is a traditional loop that uses the `in` operator to iterate over the object's own enumerable properties (including symbols, if supported by the browser).
2. **`keys+forEach`**: This approach uses the `Object.keys()` method to get an array of the object's property names and then iterates over this array using the `forEach()` method.

**Options being compared**

The benchmark compares the performance of these two approaches on a single object with 1000 properties, where each property has a value. The test aims to measure which approach is faster in terms of number of executions per second.

**Pros and Cons of each approach**

1. **`for..in`**:
	* Pros:
		+ Can be more straightforward to implement for simple iterations.
		+ Does not require extra function calls or array iteration.
	* Cons:
		+ May iterate over symbols, even if they are not intended to be accessed in this context.
		+ Performance may vary depending on the browser and object structure.
2. **`keys+forEach`**:
	* Pros:
		+ More explicit and predictable iteration approach.
		+ Avoids potential issues with symbol iteration.
	* Cons:
		+ Requires extra function calls and array iteration, which can introduce overhead.
		+ May be slower than `for..in` due to the additional operations.

**Library used in test cases**

There is no explicit library mentioned in the benchmark definition or individual test cases. However, the use of `Object.keys()` suggests that modern JavaScript environments (including browsers) provide this method as part of their API.

**Special JS feature or syntax**

There are no specific features or syntax used beyond what is necessary for the benchmark itself. The code examples provided are straightforward and do not demonstrate any advanced JavaScript concepts.

**Other alternatives**

If you need to iterate over an object's properties, other approaches might include:

1. **`Object.entries()`**: A more recent method that returns an array of key-value pairs, which can be iterated using `forEach()`.
2. **`for...of` loop**: A newer iteration syntax that is similar to `for..in` but provides better support for symbol properties.
3. **`Array.prototype.forEach.call()`**: A more generic approach that uses the `forEach()` method on an array of property names, which can be useful if you need to iterate over multiple objects.

Keep in mind that the choice of iteration approach ultimately depends on your specific use case and performance requirements.

Latest run results:

Run details: (Test run date: 6 years ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/66.0.3359.181 Safari/537.36

Browser/OS: Chrome 66 on Mac OS X 10.13.0

View result in a separate tab

Test name	Executions per second
for..in	3158.6 Ops/sec
keys+forEach	3018.4 Ops/sec

Related benchmarks:

for..in or keys+forEach (version: 1)

Comparing performance of: for..in vs keys+forEach

Created: 7 years ago by: Registered User

Jump to the latest result

for..in

keys+forEach

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 25 days ago):