Benchmark: instanceof Array vs Array.isArray()

Script Preparation code:

var arr = new Array(1000).fill(null);
for(let i = 0; i < arr.length; i++) {
	if(i % 3 === 0) {
    	arr[i] = [1];
    } else if(i % 2 === 0) {
    	arr[i] = {a: 1};
    } else {
      arr[i] = '1';
    }
}

Tests:

instanceof Array
let circle = 5; while(circle > 0) { const check = arr.map(item => item instanceof Array); circle--; }
Array.isArray()
let circle = 5; while(circle > 0) { const check = arr.map(item => Array.isArray(item)); circle--; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
instanceof Array
Array.isArray()

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/127.0.0.0 Safari/537.36

Browser/OS: Chrome 127 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
instanceof Array	2815.7 Ops/sec
Array.isArray()	2878.6 Ops/sec

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

LLMs can make mistakes. Check important info.

I'd be happy to help explain the benchmark and its results.

**Benchmark Definition**

The benchmark is designed to compare two approaches for checking if an object is an array in JavaScript:

1. Using the `instanceof` operator (`instanceof Array`)
2. Using the `Array.isArray()` method

The benchmark creation code creates a large array of 1000 elements, fills it with different types of values (null, arrays, objects, and strings), and then uses a while loop to iterate over the array.

**Options Compared**

The two options being compared are:

1. **`instanceof Array`**: This operator checks if an object is a direct instance of the `Array` class.
2. **`Array.isArray()`**: This method returns a boolean value indicating whether the given value is an array or not.

**Pros and Cons of Each Approach**

* **`instanceof` operator**:
	+ Pros:
		- Simple and efficient
		- Works well for checking if an object is a direct instance of `Array`
	+ Cons:
		- Can be slower than using `Array.isArray()` because it involves a type check
		- May not work as expected if the object has inherited properties from `Array`
* **`Array.isArray()` method**:
	+ Pros:
		- Faster and more efficient than using `instanceof`
		- Handles cases where the object is an array-like value (e.g., a string that can be iterated over)
	+ Cons:
		- May return incorrect results if the input is not a valid array
		- Less readable in some cases, as it's not immediately clear what the method does

**Library**

There is no explicit library mentioned in the benchmark definition. However, the `Array.isArray()` method is a built-in JavaScript method.

**Special JS Feature or Syntax**

The benchmark uses a feature called "array destructuring" (not explicitly used in this case, but implied by the use of `arr.map()`) and also uses modern JavaScript syntax such as arrow functions (`=>`), template literals (`\r\n`), and the `for...of` loop (not explicitly used in this case).

**Other Considerations**

The benchmark is designed to test the performance difference between these two approaches on a large array of mixed data types. The use of a while loop with a decreasing counter (`circle--`) creates a microbenchmark that can be executed multiple times, allowing for accurate measurements.

**Alternatives**

If you were to create a similar benchmark, you could consider using other methods or libraries to check if an object is an array, such as:

* Using `typeof` operator to check the type of the object (`typeof obj === 'object' && Array.isArray(obj)`)
* Using a library like Lodash's `isArray()` function
* Creating a custom function to check if an object is an array (e.g., using regex or a more complex algorithm)

Keep in mind that the best approach will depend on the specific use case and requirements of your project.

Related benchmarks:

instanceof Array vs Array.isArray() (version: 0)

Comparing performance of: instanceof Array vs Array.isArray()

Created: 5 years ago by: Guest

Jump to the latest result

instanceof Array

Array.isArray()

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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