Benchmark: object iteration

Script Preparation code:

var myObject = {
  one: 1,
  two: 2,
  three: 3,
  four: 4,
  five: 5,
  six: 6,
  seven: 7,
  eight: 8,
  nine: 9,
  ten: 10,
}

Tests:

for (var key...)
let total = 0; for (var key in myObject) { total += myObject[key]; }
direct call
let total = 0; total += myObject['one']; total += myObject['two']; total += myObject['three']; total += myObject['four']; total += myObject['five']; total += myObject['six']; total += myObject['seven']; total += myObject['eight']; total += myObject['nine']; total += myObject['ten'];

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
for (var key...)
direct call

Fastest: N/A

Slowest: N/A

Autogenerated LLM Sumamry (model llama3.2:3b, generated 19 days ago):

LLMs can make mistakes. Check important info.

**Benchmark Explanation**

The provided JSON represents a JavaScript microbenchmark, specifically designed to measure the performance of iterating over an object's properties using two different approaches: `for...in` loop and direct property access.

**Approach 1: For...in Loop (`"for (var key in myObject) {...}"`)**

This approach uses the `for...in` loop to iterate over the object's properties. The loop iterates over each property name in the object, allowing you to access both the property name and its value.

Pros:

* Easier to read and maintain, as it explicitly separates the property name from its value.
* Can be used with any type of object, including arrays and objects that have inherited properties.

Cons:

* Can iterate over inherited properties, which may not be desirable in some cases.
* May incur a performance overhead due to the loop's additional complexity.

**Approach 2: Direct Property Access (`"total += myObject['one'];..."`)**

This approach uses direct property access to access each property value. The property name is used as an index to access the corresponding value in the object.

Pros:

* Typically faster than the `for...in` loop, as it involves a single memory access operation.
* Does not iterate over inherited properties.

Cons:

* Can be less readable and maintainable, especially for complex objects or large numbers of properties.
* May require explicit management of property names to avoid typos or indexing errors.

**Library/External Functionality**

There is no library or external functionality used in this benchmark. The benchmark only involves JavaScript syntax and built-in features.

**Special JS Features/Syntax**

None of the approaches mentioned above use any special JavaScript features or syntax beyond standard ES6 syntax. However, it's worth noting that `for...in` loops can sometimes be slower than direct property access due to various factors like browser optimizations, JIT compilation, or other complexities. The benchmark aims to isolate this performance difference.

**Other Alternatives**

If you were to iterate over an object's properties in a different way, some alternatives might include:

* Using `Object.keys()` and `forEach()`: This approach uses the `Object.keys()` method to get an array of property names and then iterates over it using `forEach()`. While this approach avoids inherited properties, it may incur additional overhead due to the need for additional function calls.
* Using `for...of` loops with `entries()` or `values()`: These approaches use iterators to iterate over objects, but they might not be suitable for all types of objects.

Keep in mind that each alternative has its own trade-offs and performance characteristics. The provided benchmark aims to provide a simple, straightforward comparison between two common approaches to iterating over objects in JavaScript.

Latest run results:

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

User agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:61.0) Gecko/20100101 Firefox/61.0

Browser/OS: Firefox 61 on Windows 7

View result in a separate tab

Test name	Executions per second
for (var key...)	1679871.6 Ops/sec
direct call	16798766.0 Ops/sec

Related benchmarks:

object iteration (version: 0)

iterate over an objects props

Comparing performance of: for (var key...) vs direct call

Created: 6 years ago by: Registered User

Jump to the latest result

for (var key...)

direct call

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Sumamry (model llama3.2:3b, generated 19 days ago):