Benchmark: For in vs Object.keys.forEach

Script Preparation code:

var obj = new Object()
var keys = (new Array(100)).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:

Run details: (Test run date: one year ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/131.0.0.0 Safari/537.36

Browser/OS: Chrome 131 on Windows

View result in a separate tab

Test name	Executions per second
For In	2263.6 Ops/sec
Object keys forEach	2106.5 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 and explore what's being tested in this particular benchmark.

**Benchmark Definition**

The provided JSON represents a benchmark test case named "For in vs Object.keys.forEach". This benchmark compares two approaches to iterate over an object:

1. **For...in**: A traditional loop that iterates over the object's own enumerable properties (i.e., excluding inherited properties).
2. **Object.keys() + forEach**: A combination of using `Object.keys()` to get an array of the object's property names and then iterating over it using the `forEach` method.

**Options Being Compared**

The two options being compared are:

* For...in: This approach iterates over the object's properties by name, checking if each property is an own enumerable property using `obj.hasOwnProperty(key)`. The loop variable `key` takes on the value of each property name in turn.
* Object.keys() + forEach: This approach uses the `Object.keys()` method to get an array of the object's property names and then iterates over it using the `forEach` method. The callback function passed to `forEach` is executed for each property name in the array.

**Pros and Cons**

Here are some pros and cons of each approach:

* For...in:
	+ Pros:
		- Simple and straightforward to implement.
		- Can be more efficient for small objects with few properties, as it avoids creating an array of property names.
	+ Cons:
		- May iterate over inherited properties (non-enumerable properties), which can lead to unexpected behavior if not handled properly.
		- Can be slower due to the additional checks (`obj.hasOwnProperty(key)`) and potentially slower loop variable lookups.
* Object.keys() + forEach:
	+ Pros:
		- More efficient for large objects with many properties, as it creates an array of property names once and then iterates over it in a more predictable manner.
		- Avoids the potential issues with inherited properties.
	+ Cons:
		- Requires creating an array of property names, which can be slower than simply iterating over the object's properties directly.
		- May require additional memory allocation for the array.

**Library and Purpose**

In this benchmark, neither library is explicitly mentioned. However, it's worth noting that `Object.keys()` is a part of the ECMAScript standard, so it's not specific to any particular library or framework.

**Special JS Features/Syntax**

There are no special JavaScript features or syntax used in this benchmark. The code uses standard ECMAScript 2015+ syntax and does not employ any experimental features or polyfills.

**Alternatives**

Other alternatives for iterating over objects in JavaScript include:

* Using a `for...of` loop (ECMAScript 2017+) which is similar to the For...in approach but provides better support for arrays and other iterable types.
* Using the `entries()` method of objects, which returns an iterator over the object's own enumerable properties and values. This approach avoids the need to create an array of property names or use `hasOwnProperty()`.
* Using a library like Lodash, which provides various iteration methods, including `forEach()`, `map()`, and `reduce()`.

These alternatives may offer different trade-offs in terms of performance, readability, and maintainability, depending on the specific use case.

Related benchmarks:

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

Comparing performance of: For In vs Object keys forEach

Created: 7 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

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