Benchmark: spread vs assign in loop

Tests:

with spread
let items = new Array(20000).fill(0); const res = items.reduce((acc, item, i) => ({ ...acc, foo: i }), {});
with Object.assign
let items = new Array(20000).fill(0); const res = items.reduce((acc, item, i) => Object.assign(acc, { foo: i }), {});
with simple assign
let items = new Array(20000).fill(0); const res = items.reduce((acc, item, i) => { acc.foo = i; return acc; }, {});

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
with spread
with Object.assign
with simple assign

Fastest: N/A

Slowest: N/A

Latest run results:

No previous run results

This benchmark does not have any results yet. Be the first one to run it!

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

LLMs can make mistakes. Check important info.

Let's break down what is being tested in this benchmark.

**Benchmark Definition**

The benchmark compares three approaches for reducing an array of 20,000 elements:

1. Using the spread operator (`{ ...acc, foo: i }`)
2. Using `Object.assign()` to mutate the accumulator object (`Object.assign(acc, { foo: i })`)
3. Using simple assignment to update a single property on the accumulator object (`acc.foo = i; return acc`)

**Options Compared**

The benchmark tests three different approaches:

* **Spread Operator**: This approach uses the spread operator to create a new object that inherits from the accumulator object `acc`. The new object is then returned as the result of the reduction.
	+ Pros: Efficient and concise way to update an object with new properties.
	+ Cons: Creates a new object on each iteration, which can lead to increased memory usage.
* **Object.assign()**: This approach uses the `Object.assign()` method to mutate the accumulator object `acc` by adding a new property `foo` with value `i`. The updated accumulator object is then returned as the result of the reduction.
	+ Pros: Modifies the existing accumulator object, reducing memory allocation.
	+ Cons: Less concise and less readable than the spread operator approach.
* **Simple Assignment**: This approach uses simple assignment to update a single property on the accumulator object `acc`. The updated accumulator object is then returned as the result of the reduction.
	+ Pros: Most efficient in terms of memory usage, but may not be as readable or maintainable.
	+ Cons: Can lead to magic numbers and less intuitive code.

**Library Usage**

The benchmark uses the built-in JavaScript `Array.prototype.reduce()` method, which is a part of the standard library. This method applies a user-supplied function to each element in an array, reducing it to a single output value.

**Special JS Features/Syntax**

There are no special JavaScript features or syntax used in this benchmark beyond what's commonly available in modern JavaScript implementations.

**Other Considerations**

When choosing between these approaches, consider the trade-offs between memory usage, readability, and performance. For most use cases, the spread operator approach is a good balance between efficiency and conciseness. However, if memory allocation needs to be optimized for extremely large datasets, the simple assignment approach might be preferable.

**Alternatives**

Some alternative approaches that could be tested in this benchmark include:

* Using `Array.prototype.map()` instead of `reduce()`, which would create a new array with transformed elements.
* Using a custom implementation of reduction using loops and manual memory management.
* Using a more functional programming style, such as using `Array.prototype.reduceRight()` or `Array.prototype.every()`.

It's worth noting that the benchmark is primarily focused on comparing the performance and memory usage of these three approaches. Other considerations, such as code readability and maintainability, might not be equally important in this context.

Related benchmarks:

spread vs assign in loop (version: 3)

Using spread operator vs mutating accumulator in reduce loop

Comparing performance of: with spread vs with Object.assign vs with simple assign

Created: 6 years ago by: Registered User

Jump to the latest result

with spread

with Object.assign

with simple 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):