Benchmark: JavaScript spread operator vs Object.assign 3

Script Preparation code:

var firstObject = Array.from({ length: 100 }).reduce((acc, _el, index) => {
  acc[`some_${index}`] = index; 
  return acc;
}, {});
var loading = true;

Tests:

Using the spread operator
const finalObject = { ...firstObject, loading, };
Using Object.assign
const finalObject = Object.assign({ loading }, firstObject);

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

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

Fastest: N/A

Slowest: N/A

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

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Let's dive into the provided JSON and explain what is tested on the benchmark.

The benchmark tests two approaches for creating a new object by copying an existing object with additional properties: using the JavaScript spread operator (`...`) and `Object.assign()`. The test case creates a large object `firstObject` with 100 properties, each containing an index value. Then, it defines two benchmarks:

1. **Using the spread operator**:
```javascript
const finalObject = { ...firstObject, loading: true };
```
In this approach, we use the spread operator (`...`) to create a new object `finalObject` by copying all properties from `firstObject`. We then add an additional property `loading` with value `true`.

Pros:

* Concise and expressive syntax
* Works with objects and arrays

Cons:

* Performance might be slower due to function call overhead (as of ES6)
* May lead to unexpected behavior if used incorrectly (e.g., spreading non-object values)

2. **Using Object.assign()**:
```javascript
const finalObject = Object.assign({ loading: true }, firstObject);
```
In this approach, we use the `Object.assign()` method to merge two objects: an empty object with a single property `loading` and the original object `firstObject`. The resulting object is assigned to `finalObject`.

Pros:

* Well-established API
* Works with any type of object (not just primitive values)

Cons:

* Requires more code than the spread operator approach
* May be slower due to method call overhead

In both cases, we're creating a new object by copying an existing object and adding one or more properties. The difference lies in the syntax and performance implications.

**Library usage:**

There is no library explicitly mentioned in the provided JSON. However, it's worth noting that `Object.assign()` is a built-in method in JavaScript since ES5.

**Special JS feature or syntax:**

The spread operator (`...`) was introduced in ES6 and allows object spreading, which enables creating new objects by copying existing properties. It's a concise and expressive way to create new objects but can lead to unexpected behavior if not used carefully.

**Alternative approaches:**

Other alternatives for creating new objects with additional properties include:

* Using the `lodash` library's `cloneDeep()` method
* Using the `immer` library's `produce()` function
* Manual property copying using a loop or recursion

Keep in mind that these alternative approaches may have different performance characteristics, syntax complexities, and use cases compared to the spread operator and `Object.assign()` methods.

Related benchmarks:

JavaScript spread operator vs Object.assign 3 (version: 0)

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

Created: 5 years ago by: Guest

Jump to the latest result

Using the spread operator

Using Object.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):