Benchmark: JS insert at index spread vs Splice

Script Preparation code:

const ITERATIONS = 500000;
var index = ITERATIONS/2;
var n = Math.random();

var list = [];
for (let i = 0; i < length; i += 1) {
  list.push(Math.random());
}

Tests:

Array update with spread operator
const clone = [ ...list.slice(0, index), n, ...list.slice(index + 1), ];
Array update with slice and assign
const clone = list.slice(); clone[index] = n;

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Array update with spread operator
Array update with slice and assign

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/130.0.0.0 Safari/537.36

Browser/OS: Chrome 130 on Windows

View result in a separate tab

Test name	Executions per second
Array update with spread operator	2640167.2 Ops/sec
Array update with slice and assign	2628476.8 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's dive into the world of JavaScript microbenchmarks!

**What is being tested?**

MeasureThat.net is testing two different approaches for inserting an element at a specific index in an array:

1. **Spread operator (`...`)**: This approach uses the spread operator to create a new array by spreading elements from two ranges: before and after the insertion point.
2. **`slice()` and assignment**: This approach uses the `slice()` method to create a shallow copy of the original array, then assigns a value to the specified index.

**Options being compared**

The benchmark is comparing the performance of these two approaches on an array of random elements. The options are:

* Insertion point: The element is inserted at a randomly chosen position within the array.
* Array size: The length of the array is randomly chosen between 100,000 and 1,000,000 elements.

**Pros and cons of each approach**

**Spread operator (`...`)**

Pros:

* More concise and expressive code
* Creates a new array without modifying the original one

Cons:

* May have higher overhead due to creating a new array
* Can be slower for very large arrays

**`slice()` and assignment**

Pros:

* May be faster for very large arrays since it only creates a shallow copy
* Allows for more control over the insertion point (e.g., copying all elements before the index)

Cons:

* More verbose code
* Modifies the original array

**Other considerations**

When choosing between these approaches, consider the following factors:

* Code readability: If you need to insert an element at a specific position frequently, the spread operator might be more concise and readable.
* Performance: For very large arrays, the `slice()` and assignment approach might be faster due to reduced overhead.

**Library usage**

There is no explicit library mentioned in the benchmark definition or test cases. However, JavaScript's built-in `Array.prototype` methods are used, such as `slice()`, `push()`, and `...` (spread operator).

**Special JS features or syntax**

The spread operator (`...`) was introduced in ECMAScript 2015 (ES6). If you're using an older version of JavaScript, this approach might not work.

**Benchmark result interpretation**

The latest benchmark results show that the `Array update with spread operator` test performed better than the `Array update with slice and assign` test. This suggests that for this specific use case, the spread operator approach is more efficient.

**Other alternatives**

If you're looking for alternative approaches or optimization techniques, consider:

* Using a custom implementation for array insertion, potentially using a cache to optimize performance.
* Exploring other JavaScript libraries or modules that provide optimized array manipulation functions (e.g., `Array.prototype.slice()`, `Array.prototype.splice()`).
* Investigating parallel execution or multi-threading to take advantage of multiple CPU cores.

Keep in mind that the choice of approach ultimately depends on your specific use case, performance requirements, and personal coding preferences.

Related benchmarks:

JS insert at index spread vs Splice (version: 0)

Comparing performance of: Array update with spread operator vs Array update with slice and assign

Created: 5 years ago by: Guest

Jump to the latest result

Array update with spread operator

Array update with slice and assign

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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