Benchmark: Object.assign vs for...in... (2)

Script Preparation code:

var target = {};
var obj = {};

for (var i = 0; i < 100; i++) {
	obj['propp'+i] = ('this is a value ' + i);
}

Tests:

Object.assign
target = {}; Object.assign(target, obj);
For in
target = {}; for (var key in obj) { target[key] = obj[key]; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Object.assign
For in

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: one year ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:129.0) Gecko/20100101 Firefox/129.0

Browser/OS: Firefox 129 on Windows

View result in a separate tab

Test name	Executions per second
Object.assign	3012485.5 Ops/sec
For in	519271.5 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 benchmark and explain what's being tested.

**Benchmark Definition**

The benchmark is comparing two approaches for copying properties from one object (`obj`) to another object (`target`): `Object.assign()` and the traditional `for...in` loop.

**Script Preparation Code**

The script preparation code creates an empty target object and an object with 100 properties, where each property has a value containing a string literal. The script is designed to make it easy for the benchmarking framework to populate the target object with properties from the source object (`obj`) in both the `Object.assign()` and `for...in` loop approaches.

**Html Preparation Code**

The html preparation code is empty, which means that the benchmark doesn't rely on any HTML-related setup or cleanup.

**Test Cases**

There are two test cases:

1. **"Object.assign"`**: This test case uses the `Object.assign()` method to copy properties from `obj` to `target`.
2. **"For in"`**: This test case uses a traditional `for...in` loop to iterate over the properties of `obj` and copy them to `target`.

**Library and Purpose**

* `Object.assign()`: The `Object.assign()` method is a part of the ECMAScript standard, which means it's supported by most modern browsers. It provides a convenient way to copy properties from one object to another.
* `for...in` loop: This is a built-in JavaScript construct that allows iterating over the properties of an object.

**Pros and Cons**

* **Object.assign()**:
	+ Pros: Fast, concise, and widely supported.
	+ Cons: May not work as expected with certain types of objects or property names (e.g., null or undefined values).
* **For in loop**:
	+ Pros: Flexible, can handle arbitrary object properties, but may be slower due to the overhead of iterating over properties using a loop.
	+ Cons: More verbose, may require additional setup or cleanup code.

**Special JS Features**

There are no special JavaScript features or syntax used in this benchmark that wouldn't be familiar to most software engineers. However, it's worth noting that the `Object.assign()` method was introduced in ECMAScript 2015 (ES6), so if you're testing older browsers, you may need to use a polyfill or alternative implementation.

**Other Alternatives**

If you want to test other approaches for copying properties from one object to another, here are some alternatives:

* `JSON.parse(JSON.stringify(obj))`: This method can be used to copy an entire object by serializing it as JSON and then parsing the resulting string back into a new object. However, this approach has limitations and may not work correctly with certain types of objects or property names.
* Destructuring assignment: This is a syntax feature introduced in ECMAScript 2015 (ES6) that allows assigning properties from an object to variables using destructuring syntax. For example: `const { prop1, prop2 } = obj;`.

Related benchmarks:

Object.assign vs for...in... (2) (version: 0)

Comparing performance of: Object.assign vs For in

Created: one year ago by: Guest

Jump to the latest result

Object.assign

For in

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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