Benchmark: JavaScript merge many properties

Script Preparation code:

const objWithManyProps1 = (function () {
  const obj = {}
  for (let i = 0; i < 100000; i++) {
    obj[`prop${i}`] = i
  }
  return obj
})()

const objWithManyProps2 = (function () {
  const obj = {}
  for (let i = 0; i < 100000; i++) {
    obj[`prop${i}`] = i
  }
  return obj
})()

Tests:

Using the spread operator
const objWithManyProps1 = (function () { const obj = {} for (let i = 0; i < 100000; i++) { obj[`prop${i}`] = i } return obj })() const objWithManyProps2 = (function () { const obj = {} for (let i = 0; i < 100000; i++) { obj[`prop${i}`] = i } return obj })() const finalObject = { ...objWithManyProps1, ...objWithManyProps2 };
Using Object.assign
const objWithManyProps1 = (function () { const obj = {} for (let i = 0; i < 100000; i++) { obj[`prop${i}`] = i } return obj })() const objWithManyProps2 = (function () { const obj = {} for (let i = 0; i < 100000; i++) { obj[`prop${i}`] = i } return obj })() const finalObject = Object.assign({}, objWithManyProps1, objWithManyProps2);
Using assignment
const objWithManyProps1 = (function () { const obj = {} for (let i = 0; i < 100000; i++) { obj[`prop${i}`] = i } return obj })() const objWithManyProps2 = (function () { const obj = {} for (let i = 0; i < 100000; i++) { obj[`prop${i}`] = i } return obj })() const finalObject = {}; for (const key in objWithManyProps1) { finalObject[key] = objWithManyProps1[key]; } for (const key in objWithManyProps2) { finalObject[key] = objWithManyProps2[key]; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Using the spread operator
Using Object.assign
Using assignment

Fastest: N/A

Slowest: N/A

Latest run results:

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

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Let's dive into the explanation of the benchmark.

**What is tested**

The provided JSON represents a JavaScript microbenchmark that tests three different approaches to merging two objects with many properties:

1. Using the spread operator (`{...objWithManyProps1, ...objWithManyProps2}`)
2. Using `Object.assign()`
3. Using simple assignment (`for (const key in objWithManyProps1) { finalObject[key] = objWithManyProps1[key]; } for (const key in objWithManyProps2) { finalObject[key] = objWithManyProps2[key]; }`)

**Options compared**

The three options are compared to determine which one is the fastest.

* **Using the spread operator**: This approach creates a new object by spreading the properties of `objWithManyProps1` and `objWithManyProps2`. It's a concise way to merge objects, but its performance may vary depending on the browser implementation.
* **Using Object.assign()**: This approach uses the `Object.assign()` method to merge the two objects. It's a widely supported method in modern browsers, but it can be slower than other approaches due to its overhead.
* **Using simple assignment**: This approach uses a simple loop to iterate over the properties of both objects and assign them to a new object (`finalObject`). While this approach may seem straightforward, it can lead to slower performance due to the iteration and property access.

**Pros and cons**

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

* **Using the spread operator**:
	+ Pros: concise and readable code
	+ Cons: might be slower in older browsers or with large objects
* **Using Object.assign()**:
	+ Pros: widely supported, efficient for small to medium-sized objects
	+ Cons: can be slower than other approaches due to its overhead
* **Using simple assignment**:
	+ Pros: potentially fast and lightweight
	+ Cons: requires explicit looping and property access, which might lead to errors

**Library usage**

None of the test cases use a specific library, but they do utilize built-in JavaScript features like `Object.assign()`.

**Special JS feature or syntax**

The benchmark doesn't mention any special JavaScript features or syntax that are unique to this scenario. The focus is on comparing different approaches to merging objects.

**Other alternatives**

There are other ways to merge objects in JavaScript, such as using `Array.prototype.reduce()`:

```javascript
const finalObject = objWithManyProps1.reduce((acc, prop) => ({ ...acc, [prop]: prop }), {})
```

Or using a library like Lodash's `merge` function:

```javascript
const finalObject = _merge({}, objWithManyProps1, objWithManyProps2);
```

However, these alternatives are not tested in this benchmark.

Overall, the benchmark provides a simple yet insightful comparison of different approaches to merging objects in JavaScript.

Related benchmarks:

JavaScript merge many properties (version: 0)

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

Created: 2 years ago by: Registered User

Jump to the latest result

Using the spread operator

Using Object.assign

Using assignment

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):