Benchmark: Dynamic property assignment vs Object.assign

Script Preparation code:

var listOfNumbers = Array(10000).fill().reduce((acc, x, i) => (acc.push(i), acc), []);

Tests:

Direct assignment
var a = listOfNumbers.reduce((acc, x) => { acc[x] = x * 2; return acc; }, {});
Object.assign
var b = listOfNumbers.reduce((acc, x) => Object.assign(acc, { [x]: x * 2 }), {});

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Direct assignment
Object.assign

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 20 days ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/131.0.0.0 Safari/537.36

Browser/OS: Chrome 131 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
Direct assignment	18269.8 Ops/sec
Object.assign	335.0 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark and explain what's being tested.

**What is being tested?**

The benchmark compares two approaches to assign properties to an object:

1. **Direct assignment**: Using the bracket notation (`[]` syntax) to dynamically assign properties to an object, like `obj[x] = x * 2`.
2. **Object.assign**: Using the `Object.assign()` method to assign properties to an object, like `Object.assign(obj, { [x]: x * 2 })`.

**Options compared**

The benchmark is comparing two options:

1. Direct assignment (using bracket notation)
2. Object.assign (using a method to assign properties)

**Pros and Cons of each approach:**

**Direct Assignment (using bracket notation)**

Pros:

* Often faster and more lightweight than using `Object.assign()`
* Can be less memory-intensive since it doesn't create an intermediate object
* Easy to read and write, as it's a common syntax in JavaScript

Cons:

* May lead to errors if the property name is not a string or a number (e.g., trying to assign a value to a non-existent property)
* Not supported by older browsers or environments that don't support bracket notation

**Object.assign()**

Pros:

* More explicit and safe, as it checks for existing properties before assigning new ones
* Works with most modern browsers and environments
* Can be used to merge multiple objects into one

Cons:

* May be slower than direct assignment due to the overhead of creating an intermediate object
* Requires more memory since it creates a new object on each execution

**Library usage:**

The benchmark doesn't use any external libraries, so no additional dependencies are involved.

**Special JS feature or syntax:**

This benchmark uses bracket notation (`[]` syntax) for dynamic property assignment, which is a common JavaScript syntax. There's no specific "special" feature being tested here; it's just a typical scenario that can be encountered in many JavaScript applications.

**Other alternatives:**

If you're looking for alternative approaches to assign properties to an object, some other options include:

* Using `Object.defineProperty()` with a getter and setter
* Using `Array.prototype.forEach()` or `Array.prototype.reduce()` with the `set` method (for older browsers that don't support modern methods)
* Using `JSON.parse()` and `JSON.stringify()` with objects (not recommended due to performance issues)

Keep in mind that these alternatives may have different trade-offs in terms of performance, memory usage, and browser compatibility.

Related benchmarks:

Dynamic property assignment vs Object.assign (version: 0)

Comparing performance of: Direct assignment vs Object.assign

Created: 3 years ago by: Registered User

Jump to the latest result

Direct assignment

Object.assign

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

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