Benchmark: Splice vs Unshift (at least addition of last elements)

Script Preparation code:

var array = [1, 2, 3, 4, 5, 6, 7, 8]

Tests:

array.splice()
array.splice(0, array.length-1, 77)
array.shift()
array.unshift(77)

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
array.splice()
array.shift()

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 22 days ago)

User agent: Mozilla/5.0 (Android 15; Mobile; rv:137.0) Gecko/137.0 Firefox/137.0

Browser/OS: Firefox Mobile 137 on Android

View result in a separate tab

Test name	Executions per second
array.splice()	14982231.0 Ops/sec
array.shift()	596108.4 Ops/sec

Autogenerated LLM Summary (model gpt-4o-mini, generated 22 days ago):

LLMs can make mistakes. Check important info.

The benchmark defined here compares the performance of two different JavaScript array methods: `splice()` and `unshift()`, both of which are used to manipulate elements in an array.

### Benchmark Overview

- **Benchmark Name**: "Splice vs Unshift (at least addition of last elements)"
- **Preparation Code**: The benchmark begins by defining an array with the values `[1, 2, 3, 4, 5, 6, 7, 8]`. This sets the context for the tests, allowing each method to operate on the same initial data set.

### Test Cases

1. **array.splice()**
   - **Benchmark Definition**: `array.splice(0, array.length-1, 77)`
   - **Test Name**: "array.splice()"
   - **Operation**: The `splice()` method is being used here to remove all elements from the start of the array (index 0) up to the second-to-last element and then insert the number `77` at the 0th index. The original contents of the array will be modified, resulting in a new array: `[77, 8]`.

2. **array.unshift()**
   - **Benchmark Definition**: `array.unshift(77)`
   - **Test Name**: "array.unshift()"
   - **Operation**: The `unshift()` method adds the number `77` to the front of the existing array. The original array is also modified, resulting in a new array: `[77, 1, 2, 3, 4, 5, 6, 7, 8]`.

### Performance Results

The benchmark results show the number of executions per second for each method on a specific environment (Firefox Mobile 137, Android):

- **array.splice()**: 14,982,231 executions per second
- **array.unshift()**: 596,108.375 executions per second

### Pros and Cons

#### `array.splice()`
- **Pros**:
  - Can modify the original array by removing and adding elements in a single call.
  - Flexible: Allows for the removal of a range of elements, giving it more functionality.
  
- **Cons**:
  - Generally slower than `unshift()` in this benchmark, likely due to the overhead of managing the removal of multiple elements along with element insertion.
  - Changes the array structure, which might not be desirable if only adding an element is required.

#### `array.unshift()`
- **Pros**:
  - Faster for adding elements at the beginning of the array, as shown in these results.
  - Very straightforward operation, specifically targeting addition.
  
- **Cons**:
  - Limited functionality; it can only add elements to the start of the array.
  - Changes the original array, which could lead to side effects if the array is used elsewhere.

### Other Considerations

- The choice between `splice()` and `unshift()` depends on the specific use case. If you are only adding an element to the front of the array and not concerned with removing elements, `unshift()` is the clear choice due to its better performance.
  
- If you require both removal and addition capabilities, then `splice()` is more appropriate, despite its slower performance.

### Alternatives

1. **Using Spread Operator**: In modern JavaScript, you might use the spread operator to create a new array by concatenating arrays or values:
   ```javascript
   let newArray = [77, ...array];
   ```
   This does not modify the original array but creates a new one instead.

2. **Using `Array.concat()`**: Similar to the spread operator, the `concat()` method can be used to create a new array:
   ```javascript
   let newArray = [77].concat(array);
   ```

Each of these alternatives prioritize immutability (creating a new array rather than modifying the existing one), which can be beneficial in functional programming paradigms and in situations where you need to maintain state without mutation. However, performance may vary based on the size of the array and the specific operation.

Related benchmarks:

Splice vs Unshift (at least addition of last elements) (version: 1)

Comparing performance of: array.splice() vs array.shift()

Created: 22 days ago by: Guest

Jump to the latest result

array.splice()

array.shift()

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model gpt-4o-mini, generated 22 days ago):