Benchmark: Replace last item in array vs spread and splice

Tests:

Spread
const items = [{id: 1, name: '1'}, {id: 2, name: '2'}, {id: 3, name: '3'}] const item = items[items.length - 1] items[items.length - 1] = { ...item, newValue: true}
Splice
const items = [{id: 1, name: '1'}, {id: 2, name: '2'}, {id: 3, name: '3'}] const item = items[items.length - 1] items.splice(-1, 1, { ...item, newValue: true})

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Spread
Splice

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 JSON and explain what's being tested.

**Benchmark Definition**

The benchmark definition is a simple JavaScript script that creates an array of objects, takes the last item from the array, updates its properties, and assigns it back to the original array. There are two approaches: using the spread operator (`...`) and using `splice()` method with three arguments (`-1`, `1`, and the new value).

**Options being compared**

The options being compared are:

* Using the spread operator (`...`) to create a new object and assign it back to the original array.
* Using the `splice()` method with three arguments to remove the last item from the array, create a new object, and insert it back into the array.

**Pros and Cons of each approach**

Using the spread operator:

Pros:

* Creates a shallow copy of the original object, which can be efficient for simple objects.
* Is often considered more readable and concise.

Cons:

* Can lead to unexpected behavior if the original object has nested properties that are also arrays or objects.

Using `splice()` method with three arguments:

Pros:

* Allows for deeper copies of objects by using multiple `splice()` calls with different indices.
* Can be faster than the spread operator for large arrays.

Cons:

* Requires more code and can be less readable due to the need to create a new object and insert it back into the array.
* Can lead to unexpected behavior if not used carefully (e.g., if the original array is modified elsewhere).

**Library/Functionality being tested**

There doesn't appear to be any external library or functionality being specifically tested. The benchmark is focused solely on comparing two different approaches to updating an object in an array.

**Special JS feature/Syntax**

The `RawUAString` field in the benchmark results suggests that the test is using a unique identifier for each browser execution, which might be related to the "User Agent" string (typically used by web browsers). However, without more context, it's difficult to determine the specific significance of this value.

**Other alternatives**

If you were to modify or extend this benchmark, some potential alternative approaches could include:

* Using `Object.assign()` instead of the spread operator.
* Using a library like Lodash's `assignInPlace()` function for deep object updates.
* Using a different data structure, such as an array of objects with nested properties, to make the comparison more challenging.

Keep in mind that these alternative approaches would require significant changes to the benchmark definition and test setup.

Related benchmarks:

Replace last item in array vs spread and splice (version: 0)

Comparing performance of: Spread vs Splice

Created: 3 years ago by: Registered User

Jump to the latest result

Spread

Splice

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):