Benchmark: Reduce and Spread vs. Foreach and Mutate (fewer, but larger, objects)

Script Preparation code:

var objectsArray = Array(10).fill(() => {
  return Object.fromEntries(Array(100).fill(() => {
    const key = Math.random().toString(36).substring(2, 5);
    const value = Math.random().toString(36).substring(2, 5);
    return [key, value];
  }));
});

Tests:

Reduce and Spread
var combined = objectsArray.reduce((memo, obj) => ({...memo, ...obj}), {});
ForEach and Mutate (for .. in loop)
var combined = {} objectsArray.forEach(obj => { for (const key in obj) { combined[key] = obj[key]; } });
Mutate with Object.assign
var combined = Object.assign(...objectsArray)
Foreach and Mutate (Object.assign)
var combined = {} objectsArray.forEach(obj => Object.assign(combined, obj));

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Reduce and Spread
ForEach and Mutate (for .. in loop)
Mutate with Object.assign
Foreach and Mutate (Object.assign)

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 3 months ago)

User agent: Mozilla/5.0 (iPhone; CPU iPhone OS 18_2_1 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) CriOS/132.0.6834.78 Mobile/15E148 Safari/604.1

Browser/OS: Chrome Mobile iOS 132 on iOS 18.2.1

View result in a separate tab

Test name	Executions per second
Reduce and Spread	1175197.1 Ops/sec
ForEach and Mutate (for .. in loop)	1089860.5 Ops/sec
Mutate with Object.assign	1723426.0 Ops/sec
Foreach and Mutate (Object.assign)	1511515.1 Ops/sec

Autogenerated LLM Summary (model llama3.2:3b, generated 6 months ago):

LLMs can make mistakes. Check important info.

Let's dive into the world of JavaScript microbenchmarks!

**Benchmark Overview**

The provided benchmark compares four different approaches to merge multiple objects in JavaScript:

1. `Reduce` with spread operator (`...`)
2. `ForEach` loop with mutation using `key`-`value` pairs
3. `Mutate` using `Object.assign()`
4. `ForEach` loop with object assignment using `Object.assign()` method

**Options Compared**

The benchmark tests the performance of each approach on a large dataset of 10 objects, each containing 100 randomly generated key-value pairs.

* **Reduce**: uses the `reduce()` method to merge objects by spreading their properties into a single object.
* **ForEach loop with mutation**: uses a `for...in` loop to iterate over the object's properties and assign values to a new object using bracket notation (`combined[key] = obj[key];`).
* **Mutate with Object.assign()**: uses the `Object.assign()` method to merge objects by copying their properties into a single object.
* **ForEach loop with Object.assign()**: similar to the previous approach, but uses the `Object.assign()` method to assign values from one object to another.

**Pros and Cons**

Here's a brief summary of the pros and cons of each approach:

1. **Reduce**: Pros: concise, efficient; Cons: may not be as readable for complex datasets.
2. **ForEach loop with mutation**: Pros: flexible, can handle nested objects; Cons: slower due to iteration and bracket notation.
3. **Mutate with Object.assign()**: Pros: simple, reliable; Cons: assumes a specific object structure (e.g., all properties are enumerable).
4. **ForEach loop with Object.assign()**: Pros: readable, avoids mutation issues; Cons: may be slower due to repeated method calls.

**Library Usage**

The benchmark uses `Object.fromEntries()` and `Array.prototype.fill()` which are part of the ECMAScript standard (ES6). No external libraries are required.

**Special JS Features/Syntax**

None mentioned in the provided code snippet. However, it's worth noting that modern JavaScript engines often use various optimizations, such as just-in-time compilation, caching, or parallel execution, which can affect benchmark results.

**Other Alternatives**

If you're interested in exploring other approaches, consider the following alternatives:

1. `Array.prototype.reduce()` with a callback function to merge objects.
2. Using a library like Lodash (which provides `merge` and `assignInPlace` functions) for more complex object merging.
3. Employing a library like Ramda (which offers `mergeBy` and `mapValues` functions) for functional programming approaches.

Please keep in mind that the best approach will depend on your specific use case, data structure, and performance requirements.

Related benchmarks:

Reduce and Spread vs. Foreach and Mutate (fewer, but larger, objects) (version: 0)

Comparing performance of: Reduce and Spread vs ForEach and Mutate (for .. in loop) vs Mutate with Object.assign vs Foreach and Mutate (Object.assign)

Created: 4 years ago by: Guest

Jump to the latest result

Reduce and Spread

ForEach and Mutate (for .. in loop)

Mutate with Object.assign

Foreach and Mutate (Object.assign)

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 6 months ago):