Benchmark: Spread operator vs. Array.map change elemet

HTML Preparation code:


<script src=''></script>

Script Preparation code:

permutations = new Array(10000).map(() => ({ pagination: 'blah blah blah' }));
var index = 500;

Tests:

Spread
let newArr = [...permutations] newArr[index] = 'NEW blah blah blah'; return newArr;
Map
const newArr = permutations.map((item, i) => { if (i === index) { return item = 'NEW blah blah blah'; } else { return item; } }) return newArr;

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Spread
Map

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: one year ago)

User agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:124.0) Gecko/20100101 Firefox/124.0

Browser/OS: Firefox 124 on Ubuntu

View result in a separate tab

Test name	Executions per second
Spread	12213.4 Ops/sec
Map	131006.9 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 definition and test cases.

**Benchmark Definition:**
The provided JSON represents a JavaScript microbenchmark that measures the performance of two approaches for modifying an array:

1. Using the spread operator (`...`).
2. Using the `Array.map()` method with a callback function.

**Options Compared:**

* **Spread Operator:** Creates a new array by spreading the elements of the original array into a new array.
	+ Pros:
		- More concise and readable code.
		- Faster execution time, since it avoids creating an intermediate array.
	+ Cons:
		- Can lead to performance issues if dealing with large arrays, as it involves creating a new array and copying elements.
* **Array.map():** Creates a new array by applying a callback function to each element of the original array.
	+ Pros:
		- More flexible, as it allows for more complex transformations.
		- Can be used in conjunction with other methods (e.g., `forEach()`).
	+ Cons:
		- Slower execution time due to the overhead of creating a new array and applying the callback function.

**Library:**
There is no explicit library mentioned in the provided JSON. However, it's worth noting that the `Array.map()` method is a built-in JavaScript method.

**Special JS Feature/Syntax:**
The benchmark uses the spread operator (`...`), which was introduced in ECMAScript 2015 (ES6). It allows for concise array creation and has become a popular feature in modern JavaScript development.

**Benchmark Preparation Code:**
The script preparation code creates an array of 10,000 objects with a `pagination` property. The `index` variable is set to 500. This data structure serves as the input for both benchmark cases.

**Individual Test Cases:**

1. **Spread Operator:**
```javascript
let newArr = [...permutations]
newArr[index] = 'NEW blah blah blah'
return newArr
```
This code uses the spread operator to create a new array, `newArr`, which is then modified by assigning a new value at index 500.

2. **Array.map():**
```javascript
const newArr = permutations.map((item, i) => {
  if (i === index) {
    return item = 'NEW blah blah blah'
  } else {
    return item
  }
})
return newArr
```
This code uses the `Array.map()` method to apply a callback function to each element of the original array. If the index matches, it assigns a new value; otherwise, it returns the original element.

**Benchmark Results:**
The latest benchmark results show that Firefox 124 performs better with the spread operator (`ExecutionsPerSecond` = 131006.90625) compared to `Array.map()` (`ExecutionsPerSecond` = 12213.3818359375).

**Other Alternatives:**

* **Using a loop:** Instead of using the spread operator or `Array.map()`, you could use a traditional `for` loop to iterate over the array and modify elements individually.
```javascript
let newArr = new Array(10000).fill(null)
for (let i = 0; i < 10000; i++) {
  if (i === index) {
    newArr[i] = 'NEW blah blah blah'
  }
}
return newArr
```
* **Using a custom library:** Depending on the specific requirements, you might consider using a specialized library like Lodash or Ramda to perform array operations. However, this would likely add overhead and may not be necessary for simple use cases.

Keep in mind that performance differences between these approaches will vary depending on factors such as array size, complexity of modifications, and specific hardware configurations.

Related benchmarks:

Spread operator vs. Array.map change elemet (version: 0)

Comparing performance of: Spread vs Map

Created: one year ago by: Guest

Jump to the latest result

Spread

Map

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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