Benchmark: JavaScript spread operator vs Object.assign performance vs merge mutation

Tests:

Using the spread operator
const firstObject = { sampleData: 'Hello world' } const secondObject = { moreData: 'foo bar' } const finalObject = { ...firstObject, ...secondObject };
Using Object.assign
const firstObject = { sampleData: 'Hello world' } const secondObject = { moreData: 'foo bar' } const finalObject = Object.assign(firstObject, secondObject);
MergeObjects function
function mergeObjects(target, source) { for (const key in source) { if (typeof source[key] === 'object' && source[key] !== null) { if (!target[key] || typeof target[key] !== 'object' || target[key] === null) { target[key] = {}; } mergeObjects(target[key], source[key]); } else { target[key] = source[key]; } } } const firstObject = { sampleData: 'Hello world' } const secondObject = { moreData: 'foo bar' } mergeObjects(firstObject, secondObject)

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Using the spread operator
Using Object.assign
MergeObjects function

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/17.4 Safari/605.1.15

Browser/OS: Safari 17 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
Using the spread operator	7531426.5 Ops/sec
Using Object.assign	7256352.0 Ops/sec
MergeObjects function	24928908.0 Ops/sec

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 its test cases.

**Benchmark Overview**

The benchmark compares the performance of three approaches to merge objects:

1. Using the spread operator (`...`)
2. Using `Object.assign()`
3. A custom `mergeObjects()` function

**Options Compared**

* Spread Operator (`...`): This syntax creates a new object with all enumerable own properties inherited from the source objects.
* `Object.assign()`: This method copies all enumerable own properties from one or more source objects to a target object.
* Custom `mergeObjects()` function: This is a custom implementation that recursively merges objects by iterating over their properties.

**Pros and Cons**

1. **Spread Operator (`...`)**:
	* Pros: Concise, readable, and works well with modern browsers.
	* Cons: Not supported in older browsers (pre-ES6), can lead to unnecessary object creation.
2. **Object.assign()**:
	* Pros: Wide browser support, efficient for large datasets.
	* Cons: Can be verbose, may not work correctly if the target or source objects have nested objects with conflicting property names.
3. **Custom `mergeObjects()` function**:
	* Pros: Flexible, can handle complex object structures and merging logic.
	* Cons: Requires custom implementation, more overhead due to recursive function calls.

**Library Usage**

The benchmark uses `Object.assign()`, which is a built-in JavaScript method. It does not rely on any external libraries.

**Special JS Features/Syntax**

There are no special JavaScript features or syntax mentioned in the benchmark code. The focus is solely on the performance comparison of the three merging approaches.

**Alternative Approaches**

Other alternatives for merging objects include:

* Using `Array.prototype.concat()` with an object constructor (e.g., `{...concat([], { ... })}`)
* Utilizing libraries like Lodash (`_.merge()`) or UglifyJS (`merge` function)
* Implementing a recursive merge function using recursion instead of iteration
* Using modern JavaScript features like `Symbol.for()` to create a unique key for each merged property

Related benchmarks:

JavaScript spread operator vs Object.assign performance vs merge mutation (version: 0)

Comparing performance of: Using the spread operator vs Using Object.assign vs MergeObjects function

Created: 2 years ago by: Guest

Jump to the latest result

Using the spread operator

Using Object.assign

MergeObjects function

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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