Benchmark: Array shallow copy - slice(0) vs conditional for() loop

Script Preparation code:

var array = [{x: 1, copy: true}, {y: 2, copy: false}, {z: 3, copy: true}, {u: 0, copy: true}, {v: -1, copy: true}, {w: -2, copy: false}];
var copy = array.map(item => Object.assign(item, {copy: false}));

Tests:

slice
copy = array.slice(0);
for loop
for (let i = 0; i < array.length; i++) { if (array[i].copy) { copy[i] = array[i]; } }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
slice
for loop

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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**Benchmark Overview**

The provided JSON represents a JavaScript microbenchmark created on MeasureThat.net. The benchmark is designed to compare the performance of two approaches for shallow copying an array: using `Array.slice(0)` or a conditional `for` loop.

**Approaches Compared**

There are two test cases:

1. **slice**: This approach uses `Array.slice(0)` to create a shallow copy of the original array.
2. **for loop**: This approach uses a conditional `for` loop to iterate over the elements of the original array, and only copies the members that have a `copy` flag set to `true`.

**Pros and Cons**

* **slice**:
	+ Pros: Simple and concise, easy to understand, and widely supported.
	+ Cons: May not be as efficient for large arrays since it creates a new array object with a reference to the original elements.
* **for loop**:
	+ Pros: Can be more flexible and efficient for large arrays, as it only copies the necessary members. However, it requires more lines of code and can be less readable.
	+ Cons: Requires careful implementation to avoid unnecessary copying or indexing.

**Library and Special Features**

There is no explicit library mentioned in the benchmark definition. However, the `Array` object is used, which is a built-in JavaScript object. No special JS features or syntax are required for this benchmark.

**Other Considerations**

* **Performance**: The performance of the two approaches may vary depending on the specific use case and array size.
* **Code Readability and Maintainability**: The simplicity and readability of the `slice` approach make it more suitable for large teams or developers who prioritize ease of maintenance.
* **Efficiency**: The `for loop` approach can be more efficient for large arrays, but requires careful implementation to avoid unnecessary copying or indexing.

**Alternatives**

Other approaches for shallow copying an array include:

1. `Array.prototype.map()`: This method creates a new array with the same length as the original array, and returns a new array object with the copied elements.
2. `Object.assign()`: This method copies all enumerable own properties of the specified object to a new object.
3. `Array.prototype.forEach()`: This method executes a function for each element in an array.

These alternatives may have different performance characteristics or trade-offs in terms of code readability and maintainability, similar to the `slice` and `for loop` approaches.

Related benchmarks:

Array shallow copy - slice(0) vs conditional for() loop (version: 0)

Is it faster to copy a whole array with slice() or only copy members with a flag that indicates copying is required?

Comparing performance of: slice vs for loop

Created: 4 years ago by: Guest

Jump to the latest result

slice

for loop

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):