Benchmark: spread vs concat

Tests:

Spread
let arr = []; let a = [1,'a',{'a':'bla'},]; arr = [...arr, ...a];
Concat
let arr = []; let a = [1,'a',{'a':'bla'},]; arr = arr.concat(a);

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Spread
Concat

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 dive into the explanation.

**Benchmark Definition**

The provided JSON represents a JavaScript microbenchmark test case named "spread vs concat". The benchmark tests two approaches to merge an array `arr` with another array `a`: using the spread operator (`...`) and concatenation (`concat()`).

**Options Compared**

The two options being compared are:

1. **Spread Operator (Spreading)**: This approach uses the spread operator (`...`) to merge the two arrays. The syntax is `arr = [...arr, ...a];`. This approach creates a new array by copying elements from both `arr` and `a`.
2. **Concatenation (Concating)**: This approach uses the `concat()` method to merge the two arrays. The syntax is `arr = arr.concat(a);`.

**Pros and Cons**

*   **Spread Operator**:
    *   Pros: More concise, readable, and efficient in modern JavaScript engines.
    *   Cons: Not supported in older browsers like Internet Explorer 11 and Safari versions prior to 7.0. 
        It's also slower than concatenation when it comes to generating the array using a for loop.

*   **Concatenation**:
    *   Pros: Wider browser support (Internet Explorer 11, older Safari versions) 
    *   Cons: Less readable and more verbose than the spread operator, which can be less efficient due to its use of intermediate arrays.

**Library/Function**

There is no explicit library mentioned in this benchmark. The two approaches rely solely on built-in JavaScript features.

**Special JS Features or Syntax**

Neither of these approaches utilizes any special JavaScript features or syntax that would be unfamiliar to most software engineers.

**Alternatives**

Other alternatives for merging arrays include using the `Array.prototype.push()` method with a loop, such as:

```javascript
arr = [];
a.forEach(x => arr.push(x));
```

However, this approach has similar performance characteristics as concatenation and is less readable than the spread operator.

For more complex cases or specific edge conditions, you can use the `reduce()` function to merge arrays, such as:

```javascript
const mergedArray = arr.reduce((acc, curr) => acc.concat(curr), []);
```

However, for this particular benchmark, the two main approaches (spread and concatenation) already provide sufficient insight into performance differences.

Latest run results:

Run details: (Test run date: 7 years ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_6) AppleWebKit/604.4.6 (KHTML, like Gecko) Version/11.0.2 Safari/604.4.6

Browser/OS: Safari 11 on Mac OS X 10.11.6

View result in a separate tab

Test name	Executions per second
Spread	23900594.0 Ops/sec
Concat	14140795.0 Ops/sec

Related benchmarks:

spread vs concat (version: 0)

Comparing performance of: Spread vs Concat

Created: 7 years ago by: Guest

Jump to the latest result

Spread

Concat

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):