Benchmark: Last item in array pop vs length - 1

Script Preparation code:

var arr = [];
for (let i = 0; i < 1000000; i++) {
  arr.push(i);
}

Tests:

pop
for (let i = 0; i < 1000; i++) { const v = arr.pop(); }
length - 1
for (let i = 0; i < 1000; i++) { const v = arr[arr.length - 1]; }

Historical Performance Data aggregated from 5 community runs

Desktop Results:

Chrome 5 runs

pop

25K/s

length - 1

9K/s

Fastest: pop (2.9x faster)

View exact numbers

✓ pop: 25,382 ops/sec
• length - 1: 8,676 ops/sec

Results show median performance across all community submissions. Run this benchmark yourself to verify on your device.

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
pop
length - 1

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: one year ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/131.0.0.0 Safari/537.36

Browser/OS: Chrome 131 on Mac OS X 10.15.7

View result in a separate tab

pop

1.0M/s

length - 1

34K/s

View exact numbers

Test name	Executions per second
✓ pop	1,043,758 Ops/sec
length - 1	34,497 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down the provided benchmarking scenario.

**Benchmark Overview**

The test is designed to compare two approaches: using `arr.pop()` and accessing the last element of an array by its index (`arr.length - 1`).

**Options Compared**

The two options being compared are:

1. **Using `arr.pop()`**: This method removes and returns the last element of the array.
2. **Accessing the last element by its index (`arr.length - 1`)**: This approach uses an integer value to access the last element of the array.

**Pros and Cons**

### Using `arr.pop()`

Pros:

* Eliminates the need to manually keep track of the array's length.
* Can be faster, as it directly removes and returns the last element.

Cons:

* May require additional memory allocation or reallocation if the array is large, as a new array needs to be created with the remaining elements.
* Can be slower due to the overhead of removing an element from the middle of the array (if it's not already empty).

### Accessing the last element by its index (`arr.length - 1`)

Pros:

* Does not require additional memory allocation or reallocation, as it only accesses a single element.
* Can be faster when dealing with large arrays, as it avoids the overhead of removing an element.

Cons:

* Requires manual keeping track of the array's length, which can lead to errors if not implemented correctly.
* May be slower due to the potential for more expensive lookups (if the index is out of bounds or not easily computable).

**Library and Special JS Feature**

There are no libraries used in this benchmark. However, note that using `arr.pop()` assumes that the array is not modified while iterating over it, as removing an element can change the indices of subsequent elements.

**Other Considerations**

* The array size used in both test cases (1 million) is quite large, which may amplify any performance differences between the two approaches.
* The loop iterations are relatively low (1000), which might not fully capture the performance characteristics of these methods with larger arrays or more complex scenarios.

**Alternatives**

Other approaches to accessing the last element of an array could include:

1. Using a custom function that returns the last element, such as `arr.get(0)`, assuming the array has at least one element.
2. Using a library like Lodash's `last` function, which is designed for this purpose.
3. Implementing a more complex data structure, such as a linked list or a doubly-linked list, where accessing elements from the end is optimized.

These alternatives might have different trade-offs in terms of performance, memory usage, and complexity, but they could provide additional insights into optimizing array access patterns.

Last item in array pop vs length - 1 (version: 0)

Comparing performance of: `pop vs length - 1`

Created: 2 years ago by: Guest

Go to the latest result

pop

length - 1

Historical Performance Data aggregated from 5 community runs

Desktop Results:

Chrome 5 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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

Last item in array pop vs length - 1 (version: 0)

Comparing performance of: pop vs length - 1

Created: 2 years ago by: Guest

Go to the latest result

pop

length - 1

Historical Performance Data aggregated from 5 community runs

Desktop Results:

Chrome 5 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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

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Comparing performance of: `pop vs length - 1`