Benchmark: Mutate vs assign

Script Preparation code:

var evaluators = [];
for(i=0; i < 1000; i++) {
  evaluators.push({ id: i });
}

Tests:

Mutating
evaluators.reduce((acc, val) => { acc[val.id] = val; return acc; }, {});
Spread
evaluators.reduce((acc, val) => { return Object.assign(acc, { [val.id]: val }); }, {});

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Mutating
Spread

Fastest: N/A

Slowest: N/A

Latest 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 break down the provided benchmark and explain what is being tested.

**Benchmark Overview**

The benchmark measures the performance difference between two approaches: mutating an object using `evaluators.reduce()` and assigning new properties to an existing object using `Object.assign()`. The test case uses a JavaScript array of objects, where each object has an "id" property.

**Options Being Compared**

There are two options being compared:

1. **Mutating**: This approach modifies the original object by adding new properties to it using the `evaluators.reduce()` method.
2. **Spread**: This approach creates a new object and assigns values from the original array of objects using `Object.assign()`, rather than modifying the original object.

**Pros and Cons of Each Approach**

1. **Mutating**:
	* Pros: Only one memory allocation is required, which can be beneficial for large datasets.
	* Cons: The original object is modified in place, which might not be desirable if the original object needs to remain unchanged.
2. **Spread**:
	* Pros: A new object is created, leaving the original object unchanged. This approach can be more predictable and safer, especially when working with complex objects or large datasets.
	* Cons: Two memory allocations are required (one for the new object and one for the original array of objects).

**Library Used**

In this benchmark, a JavaScript library called `Array.prototype.reduce()` is used to iterate over the array of objects. The `reduce()` method applies a callback function to each element in the array, reducing it to a single output value.

**Special JS Features or Syntax**

None are mentioned explicitly in this benchmark.

**Other Considerations**

*   The use of `evaluators.reduce()` and `Object.assign()` suggests that the test is more focused on performance rather than safety or predictability.
*   Since both options modify an object (albeit differently), it's essential to consider whether modifying objects is a critical aspect of this particular use case.

**Alternatives**

Other approaches to achieve similar results include:

1.  Using `forEach()` instead of `reduce()`: This would involve iterating over the array using a callback function, but it wouldn't provide the same benefits as `reduce()`.
2.  Creating a new object with `Object.fromEntries()`: Instead of using `reduce()` or `assign()`, this approach would create a new object from an array of key-value pairs.
3.  Using ES6's `for...of` loop: This would provide a more traditional and safer way to iterate over the array, without modifying it in place.

However, these alternatives may not provide the same level of performance or predictability as the original `reduce()` approach used in the benchmark.

Related benchmarks:

Mutate vs assign (version: 0)

Comparing performance of: Mutating vs Spread

Created: 7 years ago by: Guest

Jump to the latest result

Mutating

Spread

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):