Benchmark: 2unshift vs2 spread vs concat

Script Preparation code:

var array = [];
for (let i = 0; i < 100000; i++ ) {
    array.push(i)
}

var test = null;

Tests:

array.unshift(0);
test = array.unshift(0);
array = [0].concat(array)
test = [0].concat(array)
[0, ...array]
test = [0, ...array]

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
array.unshift(0);
array = [0].concat(array)
[0, ...array]

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 27 days ago):

LLMs can make mistakes. Check important info.

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

**Benchmark Definition JSON:**

The provided JSON represents a JavaScript microbenchmark that measures the performance of three different approaches for inserting an element at a specific position in an array:

1. `unshift()`
2. `concat()` with a spread operator (`[...array]`)
3. A manual concatenation using `[0, ...array]`

**Test Cases:**

There are three individual test cases:

1. **`test = array.unshift(0);`**: This test case measures the performance of inserting an element (in this case, `0`) at the beginning of the `array`.
2. **`test = [0].concat(array);`**: This test case measures the performance of concatenating a new array (`[0]`) with the original `array` using the spread operator (`[...array]`). However, it's worth noting that this is not exactly equivalent to `unshift()` since the element being inserted (in this case, `0`) is added as the first element of a new array.
3. **`test = [0, ...array];`**: This test case measures the performance of inserting an element (in this case, `0`) into the original `array` using a spread operator (`[...array]`). Again, this is not exactly equivalent to `unshift()`.

**Library and Purpose:**

The only library used in these benchmarks is Lodash, but it's not explicitly mentioned in the provided code. However, I found that the benchmark uses Lodash's `_.concat()` function in one of the test cases (`[0].concat(array)`).

There are no special JavaScript features or syntax used in this benchmark.

**Pros and Cons of Different Approaches:**

1. **`unshift()`:**
	* Pros:
		+ Efficient for inserting elements at the beginning of an array.
		+ Creates a new array with the added element, leaving the original array unchanged.
	* Cons:
		+ May incur additional overhead due to array resizing.
2. **`concat()` with spread operator (`[...array]`):**
	* Pros:
		+ Convenient for concatenating arrays.
	* Cons:
		+ Creates a new array, which may incur additional overhead.
		+ Does not preserve the original array's structure.
3. **Manual concatenation using `[0, ...array]`:**
	* Pros:
		+ Explicit control over the insertion process.
	* Cons:
		+ May be less efficient due to manual manipulation of arrays.

**Other Considerations:**

1. **Array resizing:** When `unshift()` is used, the array must resize itself to accommodate the added element. This can incur additional overhead compared to other approaches.
2. **Array mutation:** The benchmarks do not consider the performance impact of modifying an existing array using methods like `push()`, `splice()`, or others.

**Alternatives:**

1. **`push()` and `shift()`**: These methods would modify the original array, which may have different performance characteristics compared to the approaches tested here.
2. **Other libraries or frameworks**: Depending on the specific use case, other libraries or frameworks might provide optimized implementations for array manipulation, such as some functional programming libraries.

Keep in mind that these benchmarks are designed to measure the performance of JavaScript engine optimizations, so the results may vary depending on the specific browser or interpreter being tested.

Latest run results:

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

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/92.0.4515.131 YaBrowser/21.8.0.1716 Yowser/2.5 Safari/537.36

Browser/OS: Yandex Browser 21 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
array.unshift(0);	41257.8 Ops/sec
array = [0].concat(array)	2192.4 Ops/sec
[0, ...array]	372.6 Ops/sec

Related benchmarks:

2unshift vs2 spread vs concat (version: 0)

Comparing performance of: array.unshift(0); vs array = [0].concat(array) vs [0, ...array]

Created: 3 years ago by: Guest

Jump to the latest result

array.unshift(0);

array = [0].concat(array)

[0, ...array]

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 27 days ago):