Benchmark: unshift vs pop,push

HTML Preparation code:

<!--your preparation HTML code goes here-->

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();
}
var arr = [42]

Tests:

unshift
arr.unshift(7)
pop,push
var a = arr.pop();arr.push(7);arr.push(a)

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
unshift
pop,push

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 24 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
unshift	646867.2 Ops/sec
pop,push	12869432.0 Ops/sec

Autogenerated LLM Summary (model gpt-4o-mini, generated 24 days ago):

LLMs can make mistakes. Check important info.

### Benchmark Overview

The benchmark in question compares two array manipulation techniques in JavaScript: `unshift` and a combination of `pop` and `push`. The main goal is to measure and analyze the performance differences between these methods in terms of their execution speed on a specific JavaScript engine running within a mobile browser.

### Options Compared

1. **Array Unshift (`arr.unshift(7)`)**:
   - This method adds one or more elements to the beginning of an array and returns the new length of the array.
   - For example, if you have an array `[42]` and you call `arr.unshift(7)`, the array will then be `[7, 42]`.

2. **Pop and Push (`var a = arr.pop(); arr.push(7); arr.push(a)`)**:
   - This combination involves two operations: `pop` which removes the last element from an array, and `push` which adds one or more elements to the end of an array.
   - In this case, the benchmark first removes the last element (let's say `42`), stores it in a variable (`a`), pushes `7` to the end, and then pushes back the popped element, resulting in the array being `[42, 7]`.

### Pros and Cons of Each Approach

1. **Unshift**:
   - **Pros**:
     - Straightforward and easy to understand in terms of code readability.
     - Directly appends an element at the start without needing to manipulate intermediate variables.
   - **Cons**:
     - `unshift` can be less efficient, especially for larger arrays. This is because it needs to re-index all existing elements to accommodate the new items being added to the front.

2. **Pop and Push**:
   - **Pros**:
     - Generally more efficient in terms of performance, particularly for larger arrays. This method doesn't shift all elements in the array; it only manipulates the end.
     - This approach can be beneficial when dealing with a predictable pattern of elements being added and removed from the array.
   - **Cons**:
     - Slightly more complex syntax, which may impact readability for some developers unfamiliar with the logic.
     - Requires storage (in this case, the variable `a`) to hold the popped value, adding a minor overhead in terms of memory.

### Libraries and Special JS Features
- This benchmark does not utilize any external libraries; it focuses purely on built-in array methods provided by JavaScript.
- There are no special JS features or syntax being tested in this benchmark; it uses standard array methods that are part of the ECMAScript standard.

### Alternative Approaches

In addition to the methods tested in this benchmark, there are other ways to manipulate arrays that can also be considered:

1. **Spread Operator**:
   - You can use the spread operator to construct a new array directly from existing arrays: `arr = [7, ...arr]`.
   - This method allows for a more declarative approach but also carries the performance cost of creating a new array.

2. **Concat Method**:
   - Another alternative could be using `.concat()`, such as `arr = [7].concat(arr)`.
   - Similar to the spread operator, this also creates a new array, affecting performance in large arrays.

3. **Array-List Implementations/Dynamic Arrays**:
   - Depending on the use case, considering a different data structure such as linked lists or custom array implementations could provide better performance for certain operations.

### Conclusion

Ultimately, the choice between `unshift` and the combination of `pop` and `push` will largely depend on the specific requirements of your application, including the size of the array and the frequency of element insertion at the beginning. For performance-critical applications, profiling these methods in real-world scenarios is always recommended to make informed decisions.

Related benchmarks:

unshift vs pop,push (version: 1)

Comparing performance of: unshift vs pop,push

Created: 24 days ago by: Guest

Jump to the latest result

unshift

pop,push

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model gpt-4o-mini, generated 24 days ago):