Benchmark: pop vs. Index write performance

Script Preparation code:

var arr = [1];

Tests:

Array.prototype.push
arr.pop(); arr.push(1);
Index write
arr.length = arr.length - 1; arr.push(1);

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Array.prototype.push
Index write

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 28 days ago):

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark and explain what's being tested.

**Overview**

The provided benchmark compares the performance of two different approaches to update the length of an array in JavaScript: using `Array.prototype.push` or writing directly to the `length` property.

**Benchmark Definition JSON**

The benchmark definition is a simple JSON object that contains metadata about the benchmark. Here's what it says:

* `Name`: The name of the benchmark, which is "pop vs. Index write performance".
* `Description`: There is no description provided for this benchmark.
* `Script Preparation Code`: This code is executed before running each test case. It creates an array `arr` and initializes it with a single element: `[1]`.
* `Html Preparation Code`: This code is not necessary for this benchmark.

**Individual Test Cases**

There are two individual test cases in the benchmark:

1. **Array.prototype.push**: This test case runs the JavaScript expression `arr.pop();\r\narr.push(1);`. In essence, it removes the last element from the array using `pop()` and then adds a new element at the end of the array using `push()`.
2. **Index write**: This test case runs the JavaScript expression `arr.length = arr.length - 1;\r\narr.push(1);`. It decrements the length of the array by 1 and then adds a new element to the end of the array.

**Performance Comparison**

The benchmark measures the performance of these two approaches by executing each test case multiple times (in this case, not specified) and reporting the number of executions per second. The results are stored in an object that contains metadata about the browser, device platform, operating system, and more.

**Options Compared**

Two options are being compared:

1. **Array.prototype.push**: This approach uses a built-in method to add elements to the end of the array.
2. **Index write**: This approach writes directly to the `length` property of the array, modifying its internal state.

**Pros and Cons**

Here's a brief summary of the pros and cons of each approach:

* **Array.prototype.push**:
	+ Pros: More readable and maintainable code; less chance of off-by-one errors.
	+ Cons: May be slower due to method call overhead.
* **Index write**:
	+ Pros: Can be faster since it avoids method call overhead, but may require more careful handling of edge cases (e.g., incrementing the length when there are no elements).
	+ Cons: More prone to off-by-one errors and less readable code.

**Library**

In this benchmark, there is no explicit library mentioned. However, the `Array.prototype.push` method is a built-in part of JavaScript's Array prototype.

**Special JS Feature or Syntax**

There isn't any special JS feature or syntax being used in these benchmarks. They are straightforward examples that demonstrate the performance differences between two approaches to updating array length.

**Other Alternatives**

If you were to write your own benchmark, you might consider including additional test cases or variations, such as:

* Using `Array.prototype.shift()` instead of `pop()`
* Adding multiple elements at once using `push` with an array of values
* Using a different data structure (e.g., `Set`, `Map`) for the array

Keep in mind that these alternatives would require modifying the benchmark definition and test cases accordingly.

Latest run results:

Run details: (Test run date: 3 years ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_6) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/14.0.3 Safari/605.1.15

Browser/OS: Safari 14 on Mac OS X 10.15.6

View result in a separate tab

Test name	Executions per second
Array.prototype.push	14625901.0 Ops/sec
Index write	8913578.0 Ops/sec

Related benchmarks:

pop vs. Index write performance (version: 0)

Comparing performance of: Array.prototype.push vs Index write

Created: 3 years ago by: Guest

Jump to the latest result

Array.prototype.push

Index write

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 28 days ago):