Benchmark: in vs [] - MeasureThat.net

Script Preparation code:

window.test = {}
for (i = 0; i < 9999999; i++) {
    test[i] = i
}

window.value = 999999

Tests:

in checking
console.log(value in test)
includes checking
console.log(test[value] !== undefined)

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
in checking
includes checking

Fastest: N/A

Slowest: N/A

Latest run results:

No previous run results

This benchmark does not have any results yet. Be the first one to run it!

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

LLMs can make mistakes. Check important info.

I'd be happy to explain what's being tested in this JavaScript microbenchmark.

**Overview**

The benchmark is comparing two approaches for checking if an element exists in an array or object:

1. Using the `in` operator (`value in test`)
2. Using array indexing and checking for undefined (`test[value] !== undefined`)

**What is being tested?**

In the first test case, "in checking", the benchmark measures how fast it can execute a simple loop that uses the `in` operator to check if each index of the `test` object exists.

In the second test case, "includes checking", the benchmark measures how fast it can execute a similar loop but uses array indexing and checks for undefined instead of using the `in` operator.

**Options compared**

The two approaches being compared are:

* Using the `in` operator to check if an element exists in an object or array.
* Using array indexing and checking for undefined.

**Pros and Cons of each approach:**

1. **Using the `in` operator**
	* Pros:
		+ Faster, as it only needs to access the property name, not the value itself.
		+ More readable and intuitive, as it clearly conveys the intention of checking if an element exists in an object or array.
	* Cons:
		+ May not work correctly for certain types of objects (e.g., arrays with non-numeric indices).
2. **Using array indexing and checking for undefined**
	* Pros:
		+ Works correctly for arrays with non-numeric indices.
		+ Can be faster in some cases, as it only needs to access the value itself.
	* Cons:
		+ Less readable and intuitive, as it requires a separate step to check if the value is undefined.

**Library and syntax**

There is no specific library being used in this benchmark. However, note that some browsers may have additional features or optimizations that could affect the results, such as:

* Firefox's `in` operator optimization (explained below)
* Other browsers' array indexing optimizations

**Special JavaScript feature**

The `in` operator has a special behavior in Firefox, where it is optimized for certain use cases. In particular, when using `in` with an array or object, Firefox can use a technique called " property enumeration" to avoid the overhead of iterating over the entire object or array. This optimization is not enabled by default, but it can result in significant performance improvements for simple cases like this benchmark.

**Other considerations**

* The size of the input data (`test` object) and its distribution (e.g., uniform, random, etc.) may affect the results.
* Other factors that could influence the performance, such as JavaScript engine optimization techniques, memory allocation, or garbage collection, are not accounted for in this benchmark.

**Alternatives**

If you want to run a similar benchmark with different inputs or variations of these approaches, consider using other microbenchmarking frameworks or libraries, such as:

* Microbenchmark (a Node.js library)
* Benchmark (a Python library)
* JsPerf (a web-based benchmarking tool)

These alternatives can provide more flexibility and control over the benchmarking process.

Related benchmarks:

in vs [] (version: 0)

Comparing performance of: in checking vs includes checking

Created: 4 years ago by: Guest

Jump to the latest result

in checking

includes checking

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):