Benchmark: Array isArray vs instanceof

Script Preparation code:

var test = [1,2,3,4];
var c;

Tests:

Instanceof
if (test instanceof Array) { c++; }
isArray
if (Array.isArray(test)) { c++; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Instanceof
isArray

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:148.0) Gecko/20100101 Firefox/148.0

Browser/OS: Firefox 148 on Windows

View result in a separate tab

Test name	Executions per second
Instanceof	38039608.0 Ops/sec
isArray	37880952.0 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 benchmark and explain what's being tested.

**What is being tested?**

The provided JSON represents a JavaScript microbenchmark that compares two approaches to check if an object is an array: using the `Array.isArray()` method and using the `instanceof` operator. The test case creates an array `test` with four elements and assigns it to variable `c`.

**Options compared**

There are two options being compared:

1. **`Array.isArray(test)`**: This approach uses a static method on the global `Array` object to check if the input `test` is an array.
2. **`test instanceof Array`**: This approach uses the `instanceof` operator, which checks if the input `test` is a prototype of the `Array` constructor.

**Pros and Cons**

1. **`Array.isArray(test)`**
	* Pros:
		+ Faster, as it's a native method call.
		+ Can be more efficient for large arrays or complex object types.
	* Cons:
		+ May not work correctly with custom array-like objects (e.g., those with `length` and other methods).
2. **`test instanceof Array`**
	* Pros:
		+ Works with custom array-like objects, as it checks the prototype chain.
		+ Can be more accurate for certain edge cases.
	* Cons:
		+ Slower due to the dynamic nature of the `instanceof` operator.

**Other considerations**

In modern JavaScript, using `Array.isArray()` is generally preferred over `instanceof` because it's faster and more straightforward. However, if you're working with custom object types or need to account for edge cases, `instanceof` might be a better choice.

**Library usage**

There is no explicit library mentioned in the benchmark definition or test case. The `Array.isArray()` method is a global method on the `Array` constructor, and the `instanceof` operator is a built-in JavaScript operator.

**Special JS feature/syntax**

There are no special features or syntax mentioned in this benchmark. It's a straightforward comparison of two common array-checking methods.

**Other alternatives**

If you need to check if an object is an array in other scenarios, consider the following alternatives:

* `Object.prototype.toString.call(test)` (similar to `instanceof`, but with additional type checking)
* Using the `Array` constructor's `constructor` property (`test.constructor === Array`)
* Implementing a custom array-checking function using a library like Lodash or Ramda

Keep in mind that these alternatives might have different performance characteristics and use cases compared to the original benchmark.

Related benchmarks:

Array isArray vs instanceof (version: 0)

Comparing performance of: Instanceof vs isArray

Created: 6 years ago by: Guest

Jump to the latest result

Instanceof

isArray

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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