Benchmark: Object.assign vs for...in...

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

Historical Performance Data aggregated from 5 community runs

Desktop Results:

Firefox 5 runs

For in

962K/s

Object.assign

552K/s

Fastest: For in (1.7x faster)

View exact numbers

✓ For in: 962,240 ops/sec
• Object.assign: 551,550 ops/sec

Results show median performance across all community submissions. Run this benchmark yourself to verify on your device.

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: 4 months ago)

User agent: Mozilla/5.0 (X11; Linux x86_64; rv:128.0) Gecko/20100101 Goanna/6.8 PaleMoon/34.0.1

Browser/OS: Pale Moon (Firefox Variant) 34 on Linux

View result in a separate tab

For in

27K/s

Object.assign

23K/s

View exact numbers

Test name	Executions per second
✓ For in	27,327 Ops/sec
Object.assign	23,215 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 its various components.

**Benchmark Definition**
The provided JSON represents a JavaScript microbenchmark that compares two approaches: `Object.assign` and `for...in`. The benchmark aims to measure which approach is faster for assigning properties to an object.

**Options Compared**

1. **Object.assign**: This method takes two arguments, the target object and the source object. It copies all enumerable own properties from the source object to the target object.
2. **For-in Loop**: This loop iterates over each property in the `obj` object and assigns its value to a corresponding property in the `target` object.

**Pros and Cons**

* **Object.assign**
	+ Pros:
		- Concise and readable syntax
		- Efficient, as it uses native JavaScript optimized code
	+ Cons:
		- Less control over the assignment process
		- May not work correctly if source object has non-enumerable properties
* **For-in Loop**
	+ Pros:
		- More control over the assignment process (e.g., skipping certain properties)
		- Works with all objects, including those with non-enumerable properties
	+ Cons:
		- Less concise and less readable syntax
		- May be slower due to iteration overhead

**Library and Special JS Features**

There is no library or special JavaScript feature mentioned in this benchmark. The focus is solely on comparing two basic approaches for object assignment.

**Other Alternatives**

In addition to `Object.assign` and the `for-in` loop, other alternatives might include:

* Using a library like Lodash's `assignIn` method
* Using a function like `forEach` or `map` with an arrow function
* Using a more modern approach with object spread syntax (`{ ...target, ...obj }`)
* Using a different iteration mechanism, such as `for...of` or `while`

Keep in mind that the choice of alternative will depend on the specific requirements and constraints of your use case.

**Benchmark Preparation Code**

The provided script preparation code creates two objects: `target` and `obj`. The `target` object is empty, while the `obj` object has 100 properties named `proppX`, where X ranges from 0 to 99. Each property is assigned a string value constructed by concatenating 'this is a value ' with the current iteration number.

The HTML preparation code is null, indicating that no specific HTML setup or initialization is required for this benchmark.

**Latest Benchmark Result**

The latest benchmark result shows two test cases: one running the `for-in` loop and another running the `Object.assign` method. The results indicate that the `for-in` loop is faster than `Object.assign`, with execution times per second being 861,590.81 for `For in` and 532,681.38 for `Object.assign`.

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

Comparing performance of: `Object.assign vs For in`

Created: one year ago by: Guest

Go to the latest result

Object.assign

For in

Historical Performance Data aggregated from 5 community runs

Desktop Results:

Firefox 5 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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

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

Comparing performance of: Object.assign vs For in

Created: one year ago by: Guest

Go to the latest result

Object.assign

For in

Historical Performance Data aggregated from 5 community runs

Desktop Results:

Firefox 5 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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

Related benchmarks

Comparing performance of: `Object.assign vs For in`