Benchmark: For in vs For 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]))
For
for (let i = 0; i < obj.length; i++) { console.log(obj[i]) }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
For In
Object keys forEach
For

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 what's being tested in the provided benchmark.

The test cases are designed to compare three different approaches for iterating over an object: `for...in`, `Object.keys().forEach()`, and a traditional `for` loop.

**For In**

This approach uses the `for...in` statement, which iterates over an object's properties by iterating over the object itself. The code is: `for (var key in obj) { if (obj.hasOwnProperty(key)) console.log(obj[key]) }`. This method has some drawbacks:

Pros:

* Can be used when you need to iterate over both the property names and values, or when you want to access other properties of the object.
* Works with objects that have inherited properties.

Cons:

* Can be slower than the other methods because it iterates over the entire object's prototype chain, which can include unnecessary properties.
* The `hasOwnProperty` method is used to filter out inherited properties, which can be expensive.

**Object.keys().forEach()**

This approach uses the `Object.keys()` method to get an array of an object's property names, and then iterates over that array using the `forEach()` method. The code is: `Object.keys(obj).forEach(key => console.log(obj[key]))`. This method is generally faster than `for...in` because it only iterates over the object's own properties, without traversing its prototype chain.

Pros:

* Fast and efficient because it avoids iterating over the entire object's prototype chain.
* Works well with objects that have a limited number of properties.

Cons:

* Does not allow access to other properties of the object being iterated.
* May not work correctly if the object has inherited properties.

**Traditional For**

This approach uses a traditional `for` loop to iterate over an array or an object's indices. The code is: `for (let i = 0; i < obj.length; i++) { console.log(obj[i]) }`. This method is often the fastest because it works directly with arrays, which are optimized for iteration.

Pros:

* Fastest of the three approaches.
* Works well with arrays and objects that have a fixed number of properties.
* Allows access to other properties of the object being iterated.

Cons:

* Does not work with objects that do not support indexing (like some built-in objects or DOM elements).
* Requires manual indexing, which can be error-prone.

In terms of special JavaScript features or syntax, there is no significant usage here. However, it's worth noting that `for...in` and `Object.keys().forEach()` are both commonly used approaches in JavaScript for iterating over objects.

Other alternatives to consider:

* `Array.prototype.forEach()`: Similar to `Object.keys().forEach()`, but works with arrays instead of objects.
* `Array.prototype.map()`: Can be used to create a new array with the values of an object, while also providing a way to access other properties of the object being iterated.
* `Array.prototype.reduce()`: Can be used to perform aggregate operations on an object, such as summing its property values.

Ultimately, the choice of iteration method depends on the specific requirements of your project and the characteristics of the data you're working with.

Related benchmarks:

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

Comparing performance of: For In vs Object keys forEach vs For

Created: 5 years ago by: Registered User

Jump to the latest result

For In

Object keys forEach

For

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):