Benchmark: spread vs mutation vs Object.assign for forEach callback

Tests:

with spread operator
const range = (from, to) => { const output = [] for(var x = from; x < to; x++){ output.push(x) } return output } let acc = {}; range(0, 10).forEach((num) => { acc = { ...acc, [num]: num } })
with mutation
const range = (from, to) => { const output = [] for(var x = from; x < to; x++){ output.push(x) } return output } let acc = {}; range(0, 10).forEach((num) => { acc[num] = num })
with object assign
const range = (from, to) => { const output = [] for(var x = from; x < to; x++){ output.push(x) } return output } let acc = {}; range(0, 10).forEach((num) => { acc = Object.assign(acc, {[num]: num}) })

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
with spread operator
with mutation
with object assign

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 28 days ago):

LLMs can make mistakes. Check important info.

Let's dive into explaining the provided benchmark.

**Benchmark Overview**

The provided benchmark tests three approaches to updating an object within a `forEach` loop: using the spread operator (`...`), mutation (directly assigning to an array index), and `Object.assign`. The goal is to determine which approach is the most efficient.

**Options Compared**

1. **Spread Operator**: Using the spread operator (`...`) to update the object by creating a new object with merged properties.
2. **Mutation**: Directly assigning to an array index to update the object.
3. **Object.assign**: Using `Object.assign` to merge two objects, updating the original object.

**Pros and Cons of Each Approach**

1. **Spread Operator**:
	* Pros: Creates a new object with merged properties, avoids mutating the original object, can be more predictable and readable.
	* Cons: Can lead to performance issues if creating a large number of objects, as it involves function call overhead and object creation.
2. **Mutation**:
	* Pros: Fastest approach, as it only involves array indexing and assignment.
	* Cons: Mutates the original object, can be less predictable and more prone to errors, especially when dealing with nested objects or arrays.
3. **Object.assign**:
	* Pros: Efficiently merges two objects, avoids mutating the original object.
	* Cons: Can lead to performance issues if merging large objects, as it involves function call overhead and object creation.

**Other Considerations**

When choosing an approach, consider the trade-off between readability, predictability, and performance. In general, using the spread operator or `Object.assign` is more suitable for most use cases, while mutation might be acceptable in specific scenarios where speed is critical.

**Library and Special JavaScript Features Used**

None of the individual test cases rely on any external libraries or special JavaScript features.

**Benchmark Preparation Code Explanation**

The preparation code sets up a simple range function that generates an array from 0 to 10. The `forEach` loop iterates over this array, updating an accumulator object (`acc`) with each iteration. The three benchmark definitions differ only in the approach used to update `acc`.

For example, in the "with spread operator" test case:

```javascript
range(0, 10).forEach((num) => {
  acc = { ...acc, [num]: num };
});
```

This code creates a new object with merged properties using the spread operator (`...`). The original `acc` object is not mutated.

Similarly, in the "with mutation" test case:

```javascript
range(0, 10).forEach((num) => {
  acc[num] = num;
});
```

This code directly assigns to an array index (`acc[num]`) to update the object.

**Other Alternatives**

If you're looking for alternative approaches or libraries for updating objects in a `forEach` loop, consider:

1. **Lodash's _.assignIn**: A utility function that merges two objects while preserving the structure of the original object.
2. **Immutables library**: Provides immutable data structures and methods for safely updating objects without mutating them.

However, these alternatives are not typically used in basic `forEach` loops, as they introduce additional complexity and dependencies on external libraries.

Keep in mind that these explanations are general guidelines, and the optimal approach may vary depending on your specific use case and performance requirements.

Latest run results:

Run details: (Test run date: 2 years ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:98.0) Gecko/20100101 Firefox/98.0

Browser/OS: Firefox 98 on Mac OS X 10.15

View result in a separate tab

Test name	Executions per second
with spread operator	280165.7 Ops/sec
with mutation	3298943.8 Ops/sec
with object assign	460762.3 Ops/sec

Related benchmarks:

spread vs mutation vs Object.assign for forEach callback (version: 0)

Comparing performance of: with spread operator vs with mutation vs with object assign

Created: 5 years ago by: Guest

Jump to the latest result

with spread operator

with mutation

with object assign

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 28 days ago):