Benchmark: instanceof Array vs Array.isArray

Script Preparation code:

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

Tests:

instanceof Array
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 Array
isArray

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 2 months ago)

User agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/133.0.0.0 Safari/537.36

Browser/OS: Chrome 133 on Linux

View result in a separate tab

Test name	Executions per second
instanceof Array	14836868.0 Ops/sec
isArray	15638039.0 Ops/sec

Autogenerated LLM Summary (model llama3.2:3b, generated 6 months ago):

LLMs can make mistakes. Check important info.

Let's dive into the world of JavaScript microbenchmarks and explore what's tested in this specific benchmark.

**Overview**

The provided JSON represents a JavaScript microbenchmark that compares the performance of two different approaches to check if an object is an instance of `Array` or uses the `Array.isArray()` method. The test case is designed to measure which approach is faster.

**Options Compared**

Two options are compared:

1. **`instanceof Array`**: This method checks if an object is a subclass of `Array` using its prototype chain.
2. **`Array.isArray()`**: This method takes an object as an argument and returns a boolean indicating whether the object is an array or not.

**Pros and Cons**

Here's a brief analysis of each approach:

* **`instanceof Array`**:
	+ Pros: More flexible, can handle objects with nested arrays or complex prototypes.
	+ Cons: Can be slower for small arrays due to the overhead of traversing the prototype chain. Additionally, it may not work as expected with certain types of objects (e.g., those with `Array.prototype` in their prototype chain).
* **`Array.isArray()`**:
	+ Pros: Faster and more efficient than `instanceof Array`, especially for small arrays.
	+ Cons: Limited to checking if an object is an array, not handling nested arrays or complex prototypes.

**Library and Special JS Feature**

There are no libraries used in this benchmark, but the use of `var` with a semicolon (`;\r\n`) suggests that the test case may be using an older version of JavaScript (ES5+) where semicolons were required to end statements.

**Other Considerations**

When measuring performance differences between these two approaches, it's essential to consider the following factors:

* **Array size**: For small arrays, `instanceof Array` might perform better due to its flexibility. However, for larger arrays, `Array.isArray()` is likely to be faster.
* **Browser support**: Although both methods are widely supported, older browsers (e.g., Internet Explorer 8 and earlier) may not support the `Array.isArray()` method.
* **Use cases**: Depending on your specific use case, you might prefer one approach over the other. For example, if you need to check if an object is an array in a complex inheritance hierarchy, `instanceof Array` might be more suitable.

**Alternatives**

If you want to explore alternative approaches or optimizations for this benchmark, consider the following:

* **Using `Array.from()`**: You can use the `Array.from()` method to create an array from an iterable object, which can simplify the checks and potentially improve performance.
* **Caching results**: If the input data is fixed, you could cache the results of the checks to avoid repeated computations.
* **Parallel execution**: Using parallel execution techniques (e.g., Web Workers) might allow you to measure the performance difference between the two approaches more accurately.

Keep in mind that these alternatives may not necessarily improve the overall performance or accuracy of the benchmark, but they can help optimize the measurement process.

Related benchmarks:

instanceof Array vs Array.isArray (version: 0)

Comparing performance of: instanceof Array vs isArray

Created: 3 years ago by: Guest

Jump to the latest result

instanceof Array

isArray

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 6 months ago):