Benchmark: Spread operator vs unshift

Tests:

unshift
var l = ['apple', 7, 'omaha']; l.unshift('scarlett');
spread op
var l = ['apple', 7, 'omaha']; l = ['scarlett', ...l];

Historical Performance Data aggregated from 7 community runs

Desktop Results:

Chrome 7 runs

spread op

69.6M/s

unshift

27.6M/s

Fastest: spread op (2.5x faster)

View exact numbers

✓ spread op: 69,632,872 ops/sec
• unshift: 27,597,000 ops/sec

Results show median performance across all community submissions. Run this benchmark yourself to verify on your device.

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
unshift
spread op

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 18 days ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/154.0.0.0 Safari/537.36

Browser/OS: Chrome 154 on Mac OS X 10.15.7

View result in a separate tab

spread op

131.7M/s

unshift

58.1M/s

View exact numbers

Test name	Executions per second
✓ spread op	131,676,360 Ops/sec
unshift	58,119,484 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark and explain what's being tested.

**Benchmark Definition**

The benchmark definition represents two different ways to add an element to an array in JavaScript:

1. Using `Array.prototype.unshift()`: This method inserts one or more elements at the beginning of an array.
2. Using the spread operator (`...`): This operator creates a new array by copying the elements from an existing array.

**Options Compared**

The benchmark is comparing two options:

* **Using `unshift()`**: This approach creates a copy of the original array and then inserts the new element at the beginning of the copied array.
* **Using the spread operator (`...`)**: This approach uses the spread operator to create a new array with the existing elements and then adds the new element.

**Pros and Cons**

* **Using `unshift()`**:
	+ Pros: Can be efficient for adding elements at the beginning of an array, as it avoids the need to copy the entire array.
	+ Cons: Creates a temporary copy of the original array, which can be memory-intensive for large arrays. Also, if the original array is very large, this approach may not be as efficient as using the spread operator.
* **Using the spread operator (`...`)**:
	+ Pros: Efficiently creates a new array with the existing elements and adds the new element without creating a temporary copy of the original array.
	+ Cons: May require more CPU cycles to create the new array, especially for large arrays.

**Library Used**

There is no library explicitly mentioned in the benchmark definition. However, it's likely that the `Array.prototype.unshift()` method is using internal implementation details from the JavaScript engine, such as the V8 engine used by Chrome.

**Special JS Feature/Syntax**

The benchmark uses the spread operator (`...`), which was introduced in ECMAScript 2015 (ES6). The spread operator allows you to create a new array by copying elements from an existing array or other iterable sources.

**Other Considerations**

When choosing between these two approaches, consider the following factors:

* **Performance**: If you need to add many elements at the beginning of an array, using `unshift()` might be faster. However, for most cases, using the spread operator is a good choice.
* **Memory usage**: Using `unshift()` creates a temporary copy of the original array, which can increase memory usage for large arrays. The spread operator avoids this problem.
* **Readability**: Some developers may find the spread operator more readable and intuitive than using `unshift()`. However, others might prefer the explicit nature of `unshift()`.

**Other Alternatives**

If you need to add elements at the beginning of an array, other alternatives to `unshift()` include:

* Using `Array.prototype.concat()` with a new array created from the original array.
* Using `Array.prototype.slice()` followed by `Array.prototype.unshift()`.
* Using a custom implementation for your specific use case.

However, these alternatives may be less efficient or more memory-intensive than using `unshift()` or the spread operator.

Spread operator vs unshift (version: 0) Benchmark.js

Comparing performance of: `unshift vs spread op`

Created: 5 years ago by: Guest

Go to the latest result

unshift

spread op

Historical Performance Data aggregated from 7 community runs

Desktop Results:

Chrome 7 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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

Spread operator vs unshift (version: 0) Benchmark.js

Comparing performance of: unshift vs spread op

Created: 5 years ago by: Guest

Go to the latest result

unshift

spread op

Historical Performance Data aggregated from 7 community runs

Desktop Results:

Chrome 7 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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

Comparing performance of: `unshift vs spread op`