Benchmark: Array concat vs spread on big array

Tests:

spread
const a = [1,2,3,4,5,6,7,8,9,1,2,3,4,5,6,7,8,9,1,2,3,4,5,6,7,8,9,1,2,3,4,5,6,7,8,9,1,2,3,4,5,6,7,8,9,1,2,3,4,5,6,7,8,9] const b = [9,8,7,6,45,4,3,2,1] let other = [...a,...b]
concat
const a = [1,2,3,4,5,6,7,8,9,1,2,3,4,5,6,7,8,9,1,2,3,4,5,6,7,8,9,1,2,3,4,5,6,7,8,9,1,2,3,4,5,6,7,8,9,1,2,3,4,5,6,7,8,9] const b = [9,8,7,6,45,4,3,2,1] let other = a.concat(b)

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
spread
concat

Fastest: N/A

Slowest: N/A

Latest run results:

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

LLMs can make mistakes. Check important info.

**Benchmark Explanation**

The provided benchmark measures the performance difference between using the spread operator (`...`) and the `concat()` method to concatenate two large arrays.

**Benchmark Definition JSON**

The benchmark definition is a simple JSON object that specifies the name, description, script preparation code, and HTML preparation code for the test. However, in this case, both fields are empty, indicating that no specific setup or rendering of the benchmark is required.

**Individual Test Cases**

There are two individual test cases:

1. **"spread"`**: This test case uses the spread operator (`...`) to concatenate two large arrays: `a` and `b`. The resulting array is assigned to a variable called `other`.

```javascript
let other = [...a,...b];
```

2. **"concat"`**: This test case uses the `concat()` method to concatenate the same two large arrays: `a` and `b`. The resulting array is also assigned to a variable called `other`.

```javascript
let other = a.concat(b);
```

**Options Compared**

The benchmark compares the performance of two approaches:

1. **Spread Operator (`...`)**: This approach uses the spread operator to create a new array by copying elements from `a` and concatenating them with elements from `b`.
2. **Concat() Method**: This approach uses the `concat()` method to concatenate the two arrays.

**Pros and Cons**

**Spread Operator (`...`) Pros:**

* Can be more readable and concise in certain situations.
* Does not create a new array when used with literals (e.g., `[1, 2, ...3]`).

**Spread Operator (`...`) Cons:**

* Creates a new array when used with variables or expressions.
* May have performance implications due to the creation of a new array.

**Concat() Method Pros:**

* Can be more efficient in terms of memory allocation and copy operations.
* Does not create a new array when used with literals (e.g., `a.concat([1, 2])`).

**Concat() Method Cons:**

* May be less readable and less concise than the spread operator.

**Library Usage**

There is no explicit library usage in this benchmark. However, if we were to extend this benchmark to include libraries, some examples could include:

* `Array.prototype.concat()`: This method is a part of the JavaScript standard library.
* `Array.prototype.push()`: While not directly related to concatenation, this method can be used to implement a custom concat-like behavior.

**Special JS Features or Syntax**

There are no special JS features or syntax mentioned in this benchmark. However, if we were to extend this benchmark to include additional features, some examples could include:

* **Arrow functions**: Could potentially affect performance due to the lack of `this` binding.
* **Generator expressions**: Might not be supported by older browsers or environments.

**Other Alternatives**

Some alternative approaches to concatenating arrays in JavaScript include:

1. **Using `Array.prototype.slice()` and `Array.prototype.splice()`:**
```javascript
let other = a.slice(0, a.length - b.length).concat(b);
```
2. **Using `Array.prototype.reduce()`:**
```javascript
let other = a.reduce((acc, val) => acc.concat(val), []);
```
3. **Using a custom implementation**: Depending on the specific requirements and constraints of the project, a custom concatenation function could be implemented to optimize performance.

Note that these alternatives may not be as concise or readable as the original code, but they can provide alternative ways to achieve the desired result.

Related benchmarks:

Array concat vs spread on big array (version: 0)

Comparing performance of: spread vs concat

Created: 3 years ago by: Guest

Jump to the latest result

spread

concat

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):