Benchmark: Array reassign vs pop & push

Script Preparation code:

var array1 = ["foo", "bar", "baz"]
var array2 = ["foo", "bar", "baz"]

Tests:

Reassign
var lastIndex = array1.length - 1 array1[lastIndex] = array1[lastIndex] + "qux"
Pop & push
array2.push(array2.pop() + "qux")

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Reassign
Pop & push

Fastest: N/A

Slowest: N/A

Latest run results:

No previous run results

This benchmark does not have any results yet. Be the first one to run it!

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

LLMs can make mistakes. Check important info.

Let's break down the provided JSON benchmark data and explain what's being tested, compared, and the pros and cons of different approaches.

**Benchmark Overview**

The measurement being tested is the performance difference between two methods for reassigning or modifying elements in an array:

1. **Reassign**: Directly assigning a new value to the last element of the array using `array1[lastIndex] = ...`.
2. **Pop & Push**: Removing and replacing the last element from the end of the array using `push` and `pop`.

**Benchmark Preparation Code**

The script preparation code sets up two arrays, `array1` and `array2`, both initialized with an array of strings.

**Individual Test Cases**

There are two test cases:

### Reassign

* **Benchmark Definition**: Assigns a new value to the last element of `array1` using `array1[lastIndex] = ...`.
* **Test Name**: "Reassign"

### Pop & Push

* **Benchmark Definition**: Removes and replaces the last element from the end of `array2` using `push` and `pop`.
* **Test Name**: "Pop & push"

**Library and Purpose**

Neither of these test cases uses a specific JavaScript library. The operations are native to JavaScript.

**Special JS Feature or Syntax**

There is no special JavaScript feature or syntax being tested in this benchmark.

**Comparison and Options**

The two approaches differ significantly:

1. **Reassign**: Directly modifies the last element of the array, which can be an O(1) operation if the index is known.
2. **Pop & Push**: Removes and replaces the last element from the end of the array, which involves multiple operations: `pop`, `+` (concatenation), and potentially a new `push`. This sequence has a higher overhead compared to direct reassignment.

**Pros and Cons**

* **Reassign**:
	+ Pros: Simple, fast, and can be more efficient if the index is known.
	+ Cons: May not work correctly in certain situations (e.g., when using array methods like `slice()`).
* **Pop & Push**:
	+ Pros: Works with any array length, but may be slower due to additional operations.
	+ Cons: More complex and potentially slower.

**Alternative Approaches**

Other alternatives to these approaches include:

1. Using an array method like `splice()` or `unshift()`.
2. Creating a new array using `Array.from()` or `slice()`, followed by assignment.
3. Using `map()` with the identity function (e.g., `map(x => x)`).

Keep in mind that these alternatives might have different performance characteristics and use cases.

**Benchmark Result**

The latest benchmark result shows the execution speed for each test case:

* **Reassign**: 8,308,161 executions per second.
* **Pop & Push**: 12,790,599 executions per second.

This suggests that `pop` and `push` might be slightly slower in this specific scenario.

Related benchmarks:

Array reassign vs pop & push (version: 0)

Compare reassignment to the last element vs pop and push

Comparing performance of: Reassign vs Pop & push

Created: 4 years ago by: Registered User

Jump to the latest result

Reassign

Pop & push

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):