Benchmark: spread vs concat vs unshift223

Script Preparation code:

var array = new Array(10).fill(0);

Tests:

arrayUnshift123
const r = array.slice().unshift(0);
arrayConcat123
const r = array.concat([0])
arraySpread123
const r = array = [0, ...array]
reduce123
const r = array.reduce((acc, cur) => { acc.push(cur); return acc; }, [0])

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
arrayUnshift123
arrayConcat123
arraySpread123
reduce123

Fastest: N/A

Slowest: N/A

Latest run results:

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

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Let's break down the provided benchmark and explain what's being tested, compared, and their pros and cons.

**Benchmark Purpose:**
The provided benchmark compares the performance of three different methods to add an element to an array:

1. `unshift()`
2. `concat()` with a single-element array
3. Using the spread operator (`...`)

**Comparison Options:**

*   `unshift()`: Adds an element to the end of the array and shifts all subsequent elements to the right.
*   `concat()`: Creates a new array by copying the original array's elements followed by the given element (in this case, a single-element array).
*   Using the spread operator (`...`): Creates a new array with the given element(s) prepended to the existing array.

**Pros and Cons of Each Approach:**

1.  **`unshift()`**:
    *   Pros:
        *   Efficient for small arrays since it only requires updating the elements' indices.
        *   Simple implementation in most browsers.
    *   Cons:
        *   Can be slower for large arrays due to the need to shift all subsequent elements, which results in a higher number of temporary copies.
        *   Not as widely supported in older JavaScript versions or non-browser environments (e.g., Node.js).

2.  **`concat()`**:
    *   Pros:
        *   Generally faster than `unshift()`, especially for large arrays.
        *   More widely supported across different browsers and platforms, including older ones.
    *   Cons:
        *   Creates a new array object, which can be memory-intensive for large datasets.
        *   Requires two operations: one for creating the new array and another for assigning it to `r`.

3.  **Using the Spread Operator (`...`)**:
    *   Pros:
        *   Fastest approach, as it only requires a single operation to create the new array.
        *   Memory-efficient since it doesn't require copying all elements or creating multiple temporary arrays.
    *   Cons:
        *   Not supported in older JavaScript versions (before ECMAScript 2018).
        *   May not work correctly in some browser versions due to variations in their implementations.

**Library:**
None. This benchmark uses native JavaScript features and built-in array methods without relying on external libraries or frameworks.

**Special JS Feature/Syntax:**
The spread operator (`...`), introduced in ECMAScript 2018 (ES8) under the name "Rest property" and further developed as a feature called "Spread operator" or simply "spread syntax". This is used to expand an array expression into separate arguments when passing an array to a function.

**Other Alternatives:**
For creating arrays, other methods can be used instead of `unshift()`, `concat()`, or the spread operator. These include:

*   Using `Array.prototype.push()` followed by `Array.prototype.shift()`: This method updates the original array but is less efficient than using the spread operator for large datasets.
*   Creating an array with the `new` keyword and pushing elements to it: This method can be memory-intensive if you need to push many elements.

Here's a sample implementation of these alternatives:

```javascript
// Using push() followed by shift()
const result1 = new Array(10).fill(0);
result1.push(0);
let r = [];
for (let i = 9; i >= 0; i--) {
    r.push(result1[i]);
}

// Creating an array with the 'new' keyword
const result2 = new Array(10).fill(0);
r = [0, ...result2];
```

However, the spread operator remains a preferred choice due to its simplicity and efficiency.

Related benchmarks:

spread vs concat vs unshift223 (version: 0)

spread vs concat vs unshift

Comparing performance of: arrayUnshift123 vs arrayConcat123 vs arraySpread123 vs reduce123

Created: 3 years ago by: Guest

Jump to the latest result

arrayUnshift123

arrayConcat123

arraySpread123

reduce123

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):