Benchmark: Array shift vs pop

Script Preparation code:

var arr = [];
for (i = 0; i < 100000; i++) {
    arr.push(5);
}

Tests:

shift
for(i=0; i < 100000; i++){ arr.shift() }
pop
for(i=0; i < 100000; i++){ arr.pop() }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
shift
pop

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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Let's break down the provided benchmark and explain what is being tested, compared, and its pros and cons.

**Benchmark Overview**

The test case compares two approaches to remove elements from an array: `arr.shift()` (using `shift()`) and `arr.pop()` (using `pop()`).

**Array Operations**

In JavaScript, arrays are a fundamental data structure. When you remove elements from an array, the operation can be more expensive than expected due to the overhead of:

1. **Reindexing**: The browser needs to update the indices of the remaining elements after removing one.
2. **Memory reallocation**: The browser may need to allocate new memory for the reduced size of the array.

**Options Compared**

The benchmark compares two options:

1. **`shift()`**: This method removes and returns the first element from the array without modifying the array's length. When using `shift()`, the browser needs to update the indices of the remaining elements.
2. **`pop()`**: This method removes and returns the last element from the array and modifies the array's length.

**Pros and Cons**

1.  **`shift()`**:
    *   Pros:
        *   More intuitive for removing from the beginning of an array.
        *   Faster because it doesn't modify the array's length.
    *   Cons:
        *   Requires updating indices, which can be slower due to reindexing and memory reallocation.
2.  **`pop()`**:
    *   Pros:
        *   Easier because it modifies the array's length, eliminating the need for index updates.
        *   Can return any element from the end of the array, not just the first one.

However, `pop()` is generally slower than `shift()` because it requires updating the array's length and reallocations.

**Library: Lodash**

One library used in this benchmark is **Lodash**, specifically its `_.tail()` function. Although not explicitly mentioned in the provided JSON, it's likely that some test cases use a modified version of this function to access the last element of an array without modifying its size. The purpose of using Lodash or similar libraries like underscore is to provide an alternative implementation and potentially reveal different performance characteristics compared to native methods.

**Special JavaScript Features/Syntax**

There are no special JavaScript features or syntax explicitly mentioned in this benchmark, but it's worth noting that the use of modern web browsers (like Chrome 116) takes into account optimized implementations for `shift()` and `pop()`, as well as other array operations.

**Other Alternatives**

Alternatives to testing these specific benchmarks could be:

*   **Using different array sizes**: Increasing or decreasing the size of the test array can affect performance.
*   **Comparing with native methods**: Using alternative libraries like jQuery's `.splice()` method might reveal differences in performance compared to native `shift()` and `pop()`.
*   **Using different data structures**: Replacing arrays with linked lists, heaps, or other data structures could highlight the importance of array operations.

In summary, this benchmark compares two basic methods for removing elements from an array: `arr.shift()` and `arr.pop()`. The pros and cons of each method are discussed, taking into account factors like index updates and memory reallocation. By analyzing these results, you can better understand how different approaches to array operations affect performance in web browsers.

Related benchmarks:

Array shift vs pop (version: 0)

Comparing performance of: shift vs pop

Created: 4 years ago by: Registered User

Jump to the latest result

shift

pop

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):