Benchmark: Array .push() vs .unshift() + ref to last

Script Preparation code:

var arr = [], last = 0

Tests:

.unshift()
arr.unshift(42); last = arr[0]
.push()
arr.push(42); last = arr[arr.length - 1]

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
.unshift()
.push()

Fastest: N/A

Slowest: N/A

Latest run results:

No previous run results

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

LLMs can make mistakes. Check important info.

**Benchmark Explanation**

The provided benchmark measures the performance difference between two approaches: `arr.unshift()` and `arr.push()`, with a reference to the last element in the array.

**Options Compared**

Two options are compared:

1. **`arr.unshift(42); last = arr[0]`**: This approach uses the `unshift()` method to add an element to the beginning of the array, followed by assigning the value at index 0 (which is now the first element) to a variable named `last`.
2. **`arr.push(42); last = arr[arr.length - 1]`**: This approach uses the `push()` method to add an element to the end of the array, followed by assigning the value at the last index (i.e., `arr.length - 1`) to a variable named `last`.

**Pros and Cons**

**`arr.unshift()`**:

Pros:

* Can be faster for small arrays or when elements are added frequently to the beginning.
* Allows for more control over the order of operations.

Cons:

* Can be slower for large arrays due to the need to shift all existing elements to make space for the new one.
* Can cause performance issues if not used carefully, as it modifies the array in place.

**`arr.push()`**:

Pros:

* Generally faster and more efficient than `unshift()` for large arrays or when elements are added frequently to the end.
* Reduces memory allocation overhead compared to `unshift()`.

Cons:

* Can be slower for small arrays or when elements need to be added to the beginning.
* May not be as flexible in terms of control over the order of operations.

**Library and Syntax Considerations**

In this benchmark, there is no explicit library used. However, it's worth noting that JavaScript's array methods, including `push()` and `unshift()`, are part of the language itself.

There are no special JavaScript features or syntax used in this benchmark.

**Alternatives**

Other alternatives to compare performance include:

1. **Array construction using `[]` vs `new Array(size)`**: This would measure the performance difference between creating an array from scratch using the literal syntax versus using the `new` keyword.
2. **Using `Array.prototype.push()` vs `push()`**: This would measure the performance difference between calling the method on the prototype chain (i.e., `arr.push()`) versus on the instance itself (i.e., `arr.push()`).
3. **Using `Array.prototype.unshift()` vs `unshift()`**: This would measure the performance difference between calling the method on the prototype chain (i.e., `arr.unshift()`) versus on the instance itself (i.e., `arr.unshift()`).

These alternative benchmarks would provide more comprehensive insights into JavaScript array operations and their performance characteristics.

Related benchmarks:

Array .push() vs .unshift() + ref to last (version: 0)

Comparing performance of: .unshift() vs .push()

Created: 6 years ago by: Guest

Jump to the latest result

.unshift()

.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):