Benchmark: JS: foreach n push() reverse(); foreach n unshift()

Script Preparation code:

var arr = [], arr1 = [], arr2 = [];
for (var i=0; i<100; i++){
  arr.push(Math.random());
}

Tests:

forEach push() then reverse()
arr.forEach(function(item,index){ arr1.push(item); }); arr1.reverse();
forEach unshift()
arr.forEach(function(item,index){ arr2.unshift(item); });

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
forEach push() then reverse()
forEach unshift()

Fastest: N/A

Slowest: N/A

Latest run results:

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

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I'll break down the provided benchmark and explain what's being tested, compared, and considered.

**Benchmark Overview**

The test compares two approaches to iterate over an array in JavaScript:

1. `forEach` with `push()`: Iterates over the array using `forEach`, pushes each element onto a new array (`arr1`), and then reverses both arrays.
2. `forEach` with `unshift()`: Iterates over the array using `forEach`, unshifts each element onto a separate array (`arr2`).

**Comparison**

The benchmark measures the performance (in executions per second) of these two approaches on different JavaScript engines.

**Options Compared**

* `push()` vs. `unshift()`: These are two different methods to append elements to an array in JavaScript.
	+ **Pros:**
		- `push()` is generally faster and more efficient for appending elements to the end of an array, as it avoids the overhead of shifting elements in the array.
		- `unshift()` can be slower due to its need to shift elements in the array when adding a new element at the beginning.
	+ **Cons:**
		- `push()` modifies the original array, while `unshift()` creates a new array and returns it.
* Iterating over arrays using `forEach`: This is a common method for iterating over arrays in JavaScript.

**Libraries Used**

None are explicitly mentioned in the benchmark definition or test cases. However, some JavaScript engines (like SpiderMonkey used by Firefox) have built-in support for these optimizations.

**Special JS Features/Syntax**

No special JavaScript features or syntax are being tested in this benchmark. The focus is solely on comparing two common array manipulation techniques.

**Other Considerations**

* **Memory Allocation**: Both `push()` and `unshift()` allocate new memory for the appended/inserted elements, which can impact performance.
* **Array Length Growth**: When using `push()`, the length of the original array grows incrementally. With `unshift()`, the length of the original array remains constant since a new array is created.
* **Cache Locality**: For very large arrays, caching patterns may differ between `push()` and `unshift()` due to how elements are accessed in memory.

**Alternatives**

Other alternatives for iterating over arrays or manipulating array contents could include:

* `map()`, `filter()`, and `reduce()` methods for transforming array data
* Loops (e.g., `for`, `while`) for more control over iteration and indexing
* External libraries like Lodash or Underscore.js, which provide additional utility functions for array manipulation

Related benchmarks:

JS: foreach n push() reverse(); foreach n unshift() (version: 4)

Comparing performance of: forEach push() then reverse() vs forEach unshift()

Created: 5 years ago by: Registered User

Jump to the latest result

forEach push() then reverse()

forEach unshift()

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):