Benchmark: JS unshift vs slice

Script Preparation code:

var arr1 = [];
for(i=0; i<10000; i++){arr1.push(i);}
var arr2 = [];
for(i=0; i<10000; i++){arr2.push(i);}

Tests:

Unshift
arr1.shift(); var newArr1 = arr1;
Slice
var newArr2 = arr2.slice(1,10000);

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Unshift
Slice

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/133.0.0.0 Safari/537.36

Browser/OS: Chrome 133 on Linux

View result in a separate tab

Test name	Executions per second
Unshift	67869416.0 Ops/sec
Slice	406510.9 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's dive into the provided benchmark definition and test cases.

**Benchmark Definition**

The benchmark measures the performance of two JavaScript operations: `unshift` (from array `arr1`) and `slice` (on array `arr2`). The script preparation code creates two large arrays (`arr1` and `arr2`) by pushing 10,000 elements each. This simulates a scenario where an array is being appended to multiple times.

**Options Compared**

The benchmark compares the performance of:

1. **`unshift`**: A method that inserts one or more elements at the beginning of an array.
	* Pros: Can be used when adding new elements to an array from the start, like in some data structures (e.g., queues).
	* Cons: Inefficient for large arrays since it requires shifting all existing elements down to make room for the new ones.
2. **`slice`**: A method that creates a shallow copy of a portion of an array.
	* Pros: Efficient for creating a subset of an array, reducing memory allocation and copying effort.
	* Cons: Creates a new array object, which can consume additional memory.

**Other Considerations**

When choosing between `unshift` and `slice`, consider the following:

* If you need to frequently add elements to the beginning of an array, use `unshift`.
* If you need to create a subset of an array, use `slice`.

**Library Usage**

There is no explicit library usage mentioned in this benchmark. However, it's worth noting that both `Array.prototype.unshift` and `Array.prototype.slice` are built-in methods.

**Special JS Feature/Syntax**

There are no special JavaScript features or syntax used in this benchmark. The code only utilizes standard ECMAScript methods and operators.

**Alternative Approaches**

Other alternatives to compare in a benchmark for array operations might include:

1. **`concat()`**: A method that concatenates two or more arrays, creating a new array.
2. **`push()` with indexing**: Instead of using `unshift`, you could push elements at specific indices to simulate inserting at the beginning.
3. **Native `ArrayBuffer` and `View` API**: For working with large arrays in memory-efficient ways.

Keep in mind that these alternatives might have different performance characteristics or trade-offs, depending on the specific use case and requirements.

Related benchmarks:

JS unshift vs slice (version: 0)

Comparing performance of: Unshift vs Slice

Created: 7 years ago by: Guest

Jump to the latest result

Unshift

Slice

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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