Benchmark: instanceof vs regular comparison

Script Preparation code:

var dateList = [];
var currentDateTime = Date.now();
for (i = 0; i < 10000; i++) {
    var randomInt = Math.round(Math.random()); // This will randomly returns either 0 or 1.
    if (randomInt === 0) {
        dateList.push(null); // Fill the array with a null value.
    } else {
        dateList.push(addMinutes(currentDateTime, i)); // This will fill up the array with date objects.
    }
}

function addMinutes(dt, minutes) {
    return new Date(dt + minutes * 60000);
}

Tests:

Check with regular comparison
var counter = 0; for (i = 0; i < 10000; i++) { if (!!dateList[i]) { counter++; } }
Check using instanceof comparison
var counter = 0; for (i = 0; i < 10000; i++) { if (dateList[i] instanceof Date) { counter++; } }
Check using regular and instanceof comparison
var counter = 0; for (i = 0; i < 10000; i++) { if (!!dateList[i] && dateList[i] instanceof Date) { counter++; } }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Check with regular comparison
Check using instanceof comparison
Check using regular and instanceof comparison

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 3 years ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:87.0) Gecko/20100101 Firefox/87.0

Browser/OS: Firefox 87 on Mac OS X 10.15

View result in a separate tab

Test name	Executions per second
Check with regular comparison	3045.7 Ops/sec
Check using instanceof comparison	2592.9 Ops/sec
Check using regular and instanceof comparison	2309.5 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down the provided benchmarking test cases.

**Benchmark Definition**

The benchmark measures the efficiency of two different approaches to check if a value exists or is an instance of a specific type:

1. **Regular comparison**: Using `!!dateList[i]` to check if `i` is within the bounds of the `dateList` array.
2. **`instanceof` comparison**: Using `dateList[i] instanceof Date` to check if the value at index `i` in the `dateList` array is an instance of the `Date` type.

**Options being compared**

The two options being compared are:

* Regular comparison (`!!dateList[i]`)
* `instanceof` comparison (`dateList[i] instanceof Date`)

**Pros and Cons**

* **Regular comparison**:
	+ Pros: Simple, easy to understand, and widely supported by most browsers.
	+ Cons: Can be slower for large arrays, as it involves a loop and checks each element individually.
* `instanceof` comparison:
	+ Pros: Faster than regular comparison for large arrays, as it uses the optimized internal logic of the browser's JavaScript engine.
	+ Cons: Less intuitive and less widely supported by older browsers.

**Library usage**

The benchmark uses the `Date` type from the JavaScript Standard Library. The `addMinutes` function is a custom utility function that returns a new `Date` object created by adding minutes to a given date.

**Special JS features or syntax**

There are no special JavaScript features or syntax used in this benchmark, except for the use of the spread operator (`...`) which is not necessary and can be omitted. The benchmark focuses on comparing two basic approaches to existence checking.

**Other alternatives**

If you want to compare performance with other methods, you could consider using:

* **WeakMap`**: A built-in JavaScript object that provides fast membership testing.
* **Array.prototype.includes()`**: A method that checks if a value exists in an array using the optimized internal logic of the browser's JavaScript engine.

Keep in mind that the best approach depends on your specific use case and requirements. For existence checking, `instanceof` comparison might be a good choice for large arrays, while regular comparison might be sufficient for small arrays or when readability is more important than performance.

Related benchmarks:

instanceof vs regular comparison (version: 2)

We try to check if comparing value using regular existence comparison is more efficient than comparing using instanceof.

Comparing performance of: Check with regular comparison vs Check using instanceof comparison vs Check using regular and instanceof comparison

Created: 3 years ago by: Registered User

Jump to the latest result

Check with regular comparison

Check using instanceof comparison

Check using regular and instanceof comparison

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

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