Benchmark: isArray2 - MeasureThat.net

Script Preparation code:

var array = [
    [1, 2, 3],
    [1, 2, 3], undefined, [1, 2, 3]
]

function isDefined(obj) {
    return obj !== undefined
}
var isArray = Array.isArray

Tests:

Array.isArray
isArray(array[2])
Is Undefined
isDefined(array[2])
Is Undefined (fail)
isDefined(array[3])

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Array.isArray
Is Undefined
Is Undefined (fail)

Fastest: N/A

Slowest: N/A

Latest run results:

No previous run results

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

LLMs can make mistakes. Check important info.

**Overview of the Benchmark**

The provided benchmark, `isArray2`, tests the performance of three different approaches to check if an object is an array in JavaScript:

1. `Array.isArray`
2. `Object.prototype.toString` with `null` as a callback
3. `[]`.constructor` (also known as `ArrayConstructor`)
4. `instanceof Array`

These checks are compared to determine which approach is the fastest.

**Options Compared**

The benchmark compares four options:

1. `Array.isArray`: A built-in function provided by the JavaScript engine that checks if an object is an array.
2. `Object.prototype.toString` with `null` as a callback: This approach uses the `toString()` method of the Object prototype to get the constructor string of an object, and then checks if it matches a specific pattern (in this case, `[object Array]`). The `null` callback allows for more precise control over the output.
3. `[]`.constructor`: This approach uses the `constructor` property of an array literal (`[]`) to check if an object is an instance of that constructor.

**Pros and Cons**

1. **Array.isArray**:
	* Pros: Fast, reliable, and widely supported.
	* Cons: May not work correctly with objects that have a custom `toString()` method or are created using a different constructor.
2. **Object.prototype.toString** with `null` as a callback:
	* Pros: More accurate than `Array.isArray`, works with custom constructors, but may be slower due to the additional overhead of calling `toString()`.
	* Cons: Requires more code and may be less readable.
3. **[]`.constructor`**:
	* Pros: Simple, fast, and reliable for most cases. Works well even if the object's constructor is not exactly equal to `ArrayConstructor`.
	* Cons: May fail if the object has a custom `constructor` property that is not an instance of `Array`.

**Other Considerations**

1. **Library**: The benchmark uses the `lodash` library, but since it's just a simple array check, there's no specific reason why it needs to be loaded.
2. **JavaScript Features**: There are no special JavaScript features or syntax being used in this benchmark.

**Alternatives**

If you want to test similar approaches or consider alternative methods for checking if an object is an array, here are some options:

1. Using `Array.isArray` with a fallback for older browsers that don't support it.
2. Implementing your own `isArray` function using techniques like prototype inheritance or the `hasOwnProperty()` method.
3. Using a library like Lodash's `isArray` or Moment.js's `isArray`.

Keep in mind that these alternatives might have different performance characteristics, so they may not be suitable for all use cases.

**Conclusion**

In summary, this benchmark provides a useful test case to evaluate the performance of different approaches for checking if an object is an array in JavaScript. Understanding the pros and cons of each approach can help you choose the most efficient solution for your specific use case.

Related benchmarks:

isArray2 (version: 0)

Array.isArray vs Object.prototype.toString vs [].constructor vs instanceof

Comparing performance of: Array.isArray vs Is Undefined vs Is Undefined (fail)

Created: 5 years ago by: Guest

Jump to the latest result

Array.isArray

Is Undefined

Is Undefined (fail)

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):