Benchmark: Assigning new variable

HTML Preparation code:

const x = [1, 2, 3]

Script Preparation code:

/*your preparation JavaScript code goes here
To execute async code during the script preparation, wrap it as function globalMeasureThatScriptPrepareFunction, example:*/
async function globalMeasureThatScriptPrepareFunction() {
    // This function is optional, feel free to remove it.
    // await someThing();
}

Tests:

[]
arr = []
length = 0
arr.length = 0;

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
[]
length = 0

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; rv:133.0) Gecko/20100101 Firefox/133.0

Browser/OS: Firefox 133 on Windows

View result in a separate tab

Test name	Executions per second
[]	150246928.0 Ops/sec
length = 0	112235128.0 Ops/sec

Autogenerated LLM Summary (model gpt-4o-mini, generated one year ago):

LLMs can make mistakes. Check important info.

The benchmark "Assigning new variable" measures two different approaches to initializing an empty array in JavaScript. This analysis will cover the options compared, their pros and cons, and provide some general context for the implications of the results.

### Options Compared

1. **Using `arr = []`:**
   - **Benchmark Definition:** `arr = []`
   - **Test Name:** `[]`
   
   This approach initializes a new empty array by directly assigning it to a variable.

2. **Using `arr.length = 0;`:**
   - **Benchmark Definition:** `arr.length = 0;`
   - **Test Name:** `length = 0`

This method sets the `length` property of an existing array to `0`, effectively making it empty.

### Pros and Cons

#### Using `arr = []`
- **Pros:**
  - **Simplicity:** This approach is straightforward and clear, immediately indicating the intention to create a new array.
  - **Performance:** The benchmark results show that this method executes significantly faster (150,246,928 executions/second) compared to the alternative.
  
- **Cons:**
  - **Variable Scope:** If `arr` was previously defined and has existing references, using this method will not affect those references. Instead, it creates a new array, potentially leading to memory implications if not managed properly.

#### Using `arr.length = 0;`
- **Pros:**
  - **Mutability:** If `arr` already holds a reference to an array and you want to clear its contents without losing the reference, this is the preferred method. It updates the existing array in-place and may be preferable when the array is shared among multiple references.
  
- **Cons:**
  - **Less Intuitive:** This approach may not be as clear to someone unfamiliar with this JavaScript behavior. Setting the length property to zero implies mutating an existing object, which may not be immediately obvious as to its purpose.
  - **Performance:** The benchmark results show this method is slower (112,235,128 executions/second) compared to initializing a new array.

### Other Considerations
The choice between these two approaches may depend on the specific context in which they are used. If a new array is desired without any concerns for prior values, then `arr = []` is preferable. However, for cases where maintaining references to an existing array is necessary or if performance is less of a consideration, `arr.length = 0` could be used.

### Alternatives
Other alternatives to initializing or reseting an array could include:
- Using array methods such as `arr.splice(0)` or `arr.length = 0`, both of which can clear all elements of the array without creating a new instance.
- If a performance-critical application reuses arrays frequently, using `arr.splice()` with zero arguments might be considered, though it's typically slower than simply resetting the length.

In conclusion, choosing the appropriate method depends on specific requirements, including clarity, performance needs, and whether references to the original array need to be preserved. The benchmark results provide useful insights for making an informed decision in JavaScript.

Related benchmarks:

Assigning new variable (version: 1)

Comparing performance of: [] vs length = 0

Created: one year ago by: Guest

Jump to the latest result

[]

length = 0

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model gpt-4o-mini, generated one year ago):