Benchmark: Array cloning - MeasureThat.net

Script Preparation code:

function generateArray() {
    const a = [];
    for(let i = 0; i < 50; i++) {
        a.push(Math.random());
    }
    return a;
}

window.testData = [];

Tests:

Slice
window.testData.length = 0; const a = generateArray(); const cloneA = a.slice(); const cloneB = cloneA.slice(); window.testData.push(cloneA, cloneB);
Spread
window.testData.length = 0; const a = generateArray(); const cloneA = [...a]; const cloneB = [...cloneA]; window.testData.push(cloneA, cloneB);

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Slice
Spread

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.

Let's break down the provided benchmark and explain what's being tested, compared, and some pros and cons of each approach.

**Benchmark Purpose:**
The main purpose of this benchmark is to compare the performance of two different methods for shallow cloning arrays in JavaScript:

1. `slice()`
2. Spread operator (`...`)

Specifically, the benchmark tests how many elements can be cloned using these methods within a certain time frame (measured by "ExecutionsPerSecond").

**Script Preparation Code:**
The script preparation code generates an array of 50 random numbers and assigns it to the `window.testData` variable. This array will be used as the input for the benchmark.

**Html Preparation Code:**
There is no HTML preparation code provided, which means that this benchmark only focuses on JavaScript performance and does not involve any UI-related tasks or DOM manipulations.

**Individual Test Cases:**

1. **Slice Method:**
The first test case uses the `slice()` method to clone the array. The syntax is:
```javascript
const cloneA = a.slice();
```
This method returns a shallow copy of the original array, which means it only creates a new reference to the elements without modifying the original elements themselves.

Pros:

* Simple and widely supported (all modern browsers)
* Can be used for shallow cloning arrays

Cons:

* May not perform well for large arrays or deep objects
* Does not create a new object graph, only a new reference to existing elements

2. **Spread Operator Method:**
The second test case uses the spread operator (`...`) to clone the array. The syntax is:
```javascript
const cloneA = [...a];
```
This method creates a new array by copying all elements from the original array using the spread operator.

Pros:

* Creates a new object graph, which can be more efficient for large arrays or deep objects
* Is a modern and concise way to create copies of arrays

Cons:

* May not work correctly with certain types of data (e.g., `Symbol` values)
* Requires support for the spread operator (all modern browsers, but some older versions may not support it)

**Library Usage:**
There is no library usage in this benchmark. The tests only use built-in JavaScript methods and syntax.

**Special JS Features/Syntax:**
The benchmark uses a special feature of the JavaScript language known as "arrow functions." An arrow function is a concise way to define small, single-expression functions. In the script preparation code, the `generateArray()` function is defined using an arrow function:
```javascript
function generateArray() {
  // ...
}
```
This syntax is supported by all modern browsers and JavaScript engines.

**Alternative Approaches:**
Other approaches for shallow cloning arrays in JavaScript include:

* Using the `Array.prototype.slice.call()` method to create a new array from an existing one.
* Using a library like Lodash's `cloneDeep()` function, which creates a deep copy of an object (not just an array).
* Using a native WebAssembly-based array clone function (currently experimental).

Keep in mind that each approach has its own trade-offs and performance characteristics. The benchmark provided by MeasureThat.net aims to evaluate the relative performance of these different methods for shallow cloning arrays.

Related benchmarks:

Array cloning (version: 0)

Testing slice against spread for shallow cloning arrays.

Comparing performance of: Slice vs Spread

Created: 3 years ago by: Guest

Jump to the latest result

Slice

Spread

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):