Benchmark: barbar - MeasureThat.net

Script Preparation code:

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

Tests:

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

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
if (test instanceof Array) { c++; }
if (Array.isArray(test)) { c++; }

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 25 days ago):

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark definition and test cases to understand what is being tested.

**Benchmark Definition**

The benchmark definition is a JSON object that contains the script preparation code, HTML preparation code (which is null in this case), and a brief description of the benchmark. In this case, the script preparation code simply declares an array `test` with some values. The HTML preparation code is not used for this specific benchmark.

**Test Cases**

There are two test cases:

1. **`if (test instanceof Array) { c++; }`**

This test case checks if the value of `c++`, which increments a variable `c`, returns an `Array`. The JavaScript syntax `instanceof` is used to check if an object is an instance of a particular constructor.

2. **`if (Array.isArray(test)) { c++; }`**

This test case checks if the value of `c++` returns true when passed to the `Array.isArray()` function, which returns `true` if the input is an array-like object or null.

**Comparison**

The two test cases are comparing the behavior of JavaScript's built-in functions `instanceof` and `Array.isArray()`. The main difference between these two checks lies in their behavior for non-array-like objects.

*   `instanceof` will return false even if the value is an array-like object, whereas `Array.isArray()` will return true.
*   `Array.isArray()` is more permissive but may perform additional work to check if the input has the properties of an array. On the other hand, `instanceof` returns immediately without checking for these properties.

**Pros and Cons**

*   Using `instanceof`:
    *   Pros: More accurate results because it only checks if the value is a direct instance of the specified constructor.
    *   Cons: May not return true for non-array-like objects that have some array-like behavior, such as arrays created using Object.create().
*   Using `Array.isArray()`:
    *   Pros: Returns true for both direct instances and most array-like objects, which can be beneficial in certain scenarios.
    *   Cons: May perform additional work to check if the input has the properties of an array. It may not return immediately as required by some tests.

**Other Considerations**

*   In modern JavaScript engines, `Array.isArray()` is generally considered more accurate and safe to use than `instanceof` for checking if a value is an array-like object.
*   The choice between using `instanceof` and `Array.isArray()` may depend on the specific requirements of the test case.

**Library**

In this benchmark, there are no external libraries being used. All code is contained within the script preparation code provided in the benchmark definition.

**Special JS Features or Syntax**

None mentioned.

**Alternatives**

There are other ways to check if a value is an array-like object:

*   Using `typeof` operator with equality checks (`if (typeof test === 'object' && !Array.isArray(test) && typeof c++ !== 'undefined')`)
*   Checking for the presence of certain properties on the object (`if (Object.prototype.hasOwnProperty.call(test, 'length'))`)
*   Using a third-party library like Lodash's `isArrayLike()` function

Keep in mind that these alternatives may not be as straightforward or efficient as using `Array.isArray()`.

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/605.1.15 (KHTML, like Gecko) Version/16.4 Safari/605.1.15

Browser/OS: Safari 16 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
if (test instanceof Array) { c++; }	3092570.8 Ops/sec
if (Array.isArray(test)) { c++; }	3119061.2 Ops/sec

Related benchmarks:

barbar (version: 0)

foo

Comparing performance of: if (test instanceof Array) { c++; } vs if (Array.isArray(test)) { c++; }

Created: one year ago by: Guest

Jump to the latest result

if (test instanceof Array) { c++; }

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

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 25 days ago):