Benchmark: Spread vs mutating

Script Preparation code:

var array = Array.from(Array(1000).keys());

Tests:

Spread operator
array.reduce((acc, number) => ({ ...acc, [number]: null }), {});
Mutate accumulator
array.reduce((acc, number) => { acc[number] = null; return acc; }, {});
Object.assign
array.reduce((acc, number) => (Object.assign({}, acc, { [number]: null })))

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Spread operator
Mutate accumulator
Object.assign

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.

Let's dive into the explanation of the provided benchmark.

**Overview**

MeasureThat.net is a website that allows users to create and run JavaScript microbenchmarks. The benchmark you provided compares three different approaches to achieving the same goal: reducing an array using the `reduce` method with a spread operator, mutating the accumulator, and using `Object.assign`.

**Benchmark Definition JSON**

The benchmark definition json contains information about the test case:

* **Name**: "Spread vs mutating" - This is the name of the benchmark.
* **Description**: null - The description of the benchmark is empty in this case.
* **Script Preparation Code**: "var array = Array.from(Array(1000).keys());" - This code generates an array with 1000 elements, which will be used as the input for the reduction.
* **Html Preparation Code**: null - There is no HTML preparation code provided.

**Individual Test Cases**

The benchmark consists of three test cases:

1. **Spread Operator**:
	* `Benchmark Definition`: "array.reduce((acc, number) => ({ ...acc, [number]: null }), {});"
	* **Test Name**: "Spread operator" - This is the name of the test case.
2. **Mutate Accumulator**:
	* `Benchmark Definition`: "array.reduce((acc, number) => { acc[number] = null; return acc; }, {});"
	* **Test Name**: "Mutate accumulator"
3. **Object.assign**:
	* `Benchmark Definition`: "array.reduce((acc, number) => (Object.assign({}, acc, { [number]: null })))"
	* **Test Name**: "Object.assign"

**Approaches Compared**

The three test cases compare the performance of three different approaches:

1. Using a spread operator (`{ ...acc, [number]: null }`) to create a new object for each iteration.
2. Mutating the accumulator by directly assigning `null` to its property (`acc[number] = null;`).
3. Using `Object.assign` to merge two objects and add a new property.

**Pros and Cons of Each Approach**

1. **Spread Operator**:
	* Pros: Creates a new object for each iteration, which can lead to better performance due to reduced mutation.
	* Cons: May incur additional overhead due to object creation.
2. **Mutate Accumulator**:
	* Pros: Avoids the overhead of object creation, as it only updates the existing accumulator.
	* Cons: May cause issues with concurrency or parallelization, as multiple threads may try to mutate the same accumulator.
3. **Object.assign**:
	* Pros: Can be more efficient than creating new objects, especially for large arrays.
	* Cons: May lead to performance issues if the target object is large and not suitable for shallow copying.

**Libraries and Special Features**

None of the test cases use any libraries or special features beyond the standard JavaScript `Array` methods. However, the `Array.from` method is used in the script preparation code, which may be a non-standard approach depending on the specific browser or environment being tested.

**Other Alternatives**

In general, other approaches to reducing an array could include:

* Using a for loop and indexing into the array
* Using a library like Lodash or Ramda with their respective reduction functions
* Utilizing WebAssembly or other just-in-time compilation techniques

It's worth noting that the choice of approach depends on the specific use case, performance requirements, and compatibility constraints. The MeasureThat.net benchmark provides a useful insight into the relative performance of different approaches in JavaScript.

Related benchmarks:

Spread vs mutating (version: 0)

Comparing performance of: Spread operator vs Mutate accumulator vs Object.assign

Created: 8 years ago by: Guest

Jump to the latest result

Spread operator

Mutate accumulator

Object.assign

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):