Benchmark: For in vs Object.keys.forEach 10000

Script Preparation code:

var obj = new Object()
var keys = (new Array(10000)).fill(0).map((x, i) => { return i + 1 })
keys.forEach((x) => { obj['prop' + x] = x })

Tests:

For In
for (var key in obj) { if (obj.hasOwnProperty(key)) console.log(obj[key]) }
Object keys forEach
Object.keys(obj).forEach(key => console.log(obj[key]))

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
For In
Object keys forEach

Fastest: N/A

Slowest: N/A

Latest run results:

No previous run results

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

LLMs can make mistakes. Check important info.

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

**Benchmark Definition**

The benchmark is comparing two approaches to iterate over an object:

1. `for (var key in obj) { ... }` (often referred to as "for-in")
2. `Object.keys(obj).forEach(key => console.log(obj[key]))`

**For-In Loop**

The for-in loop iterates over the object's own enumerable properties using the property name as a variable (`key`). This approach has some advantages:

* It can handle objects with inherited properties, which might be desirable in certain situations.
* However, it also has some drawbacks:
	+ It relies on the object's prototype chain and may iterate over properties that are not actually part of the object itself (e.g., due to inheritance).
	+ The order of iteration is not guaranteed to be deterministic, as it depends on the order of property declaration in the prototype chain.
	+ Modern browsers may optimize or skip iterating over certain properties, which can affect performance.

**Object.keys() + forEach**

The second approach uses `Object.keys()` to get an array of the object's own enumerable property names and then iterates over this array using `forEach`. This approach is more predictable:

* It only iterates over the object's actual own properties, without considering inherited ones.
* The order of iteration is guaranteed to be deterministic (based on the order of property declaration in the source code).
* Modern browsers should not optimize or skip iterating over these properties.

**Pros and Cons**

Comparing these two approaches helps identify performance differences between them. Since for-in loops are often slower and less predictable, they might be a better choice when you need to iterate over an object's own properties but want more control over the iteration process. On the other hand, `Object.keys()` + forEach is likely to be faster and more reliable.

**Library Usage**

There is no explicit library usage in this benchmark, so we can assume it's using built-in JavaScript methods.

**Special JS Feature or Syntax**

This benchmark does not use any special JavaScript features or syntax beyond what's been described. However, some browsers might have specific optimizations or behaviors that could affect the results (e.g., Safari's `for...in` loop optimization).

**Other Alternatives**

If you wanted to try alternative approaches, here are a few examples:

1. **Array iteration**: Instead of using for-in or `Object.keys()`, you could use an array and iterate over its elements directly: `obj.props.forEach((prop) => console.log(prop))`.
2. **Iterators**: Another approach is to create an iterator over the object's properties using a custom function like this: `(function* (iterator) { for (const key in obj) yield key; })().forEach((key) => console.log(obj[key]))`.

Keep in mind that these alternatives might have different performance characteristics or requirements, so it's essential to test them individually.

Related benchmarks:

For in vs Object.keys.forEach 10000 (version: 0)

Comparing performance of: For In vs Object keys forEach

Created: 5 years ago by: Guest

Jump to the latest result

For In

Object keys forEach

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):