Benchmark: JavaScript Object.assign vs for in loop

Tests:

Object.assign
const a = { x: 'xxx', y: 1, z: null } const b = { z: 1, u: 'uuu', v: null } Object.assign(a, b);
for in loop
const a = { x: 'xxx', y: 1, z: null } const b = { z: 1, u: 'uuu', v: null } for (let prop in b) a[prop] = b[prop];

Historical Performance Data aggregated from 99 community runs

Desktop Results:

Chrome 70 runs

for in loop

25.0M/s

Object.assign

10.6M/s

Fastest: for in loop (2.4x faster)

View exact numbers

✓ for in loop: 24,967,172 ops/sec
• Object.assign: 10,609,662 ops/sec

Firefox 21 runs

for in loop

21.9M/s

Object.assign

13.7M/s

Fastest: for in loop (1.6x faster)

View exact numbers

✓ for in loop: 21,911,498 ops/sec
• Object.assign: 13,673,039 ops/sec

Mobile Results:

Chrome 8 runs

for in loop

8.0M/s

Object.assign

2.8M/s

Fastest: for in loop (2.9x faster)

View exact numbers

✓ for in loop: 8,006,107 ops/sec
• Object.assign: 2,797,740 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 loop

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 4 months ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/148.0.0.0 Safari/537.36

Browser/OS: Chrome 148 on Mac OS X 10.15.7

View result in a separate tab

for in loop

28.0M/s

Object.assign

27.2M/s

View exact numbers

Test name	Executions per second
✓ for in loop	27,998,330 Ops/sec
Object.assign	27,177,588 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 JavaScript microbenchmark on MeasureThat.net.

**Benchmark Definition**

The benchmark tests two approaches to merge two objects in JavaScript: `Object.assign()` and a traditional `for-in` loop.

**Options being compared**

Two options are compared:

1. **Object.assign()**: This is a built-in JavaScript method that merges two or more source objects into a target object.
2. **For-in loop**: This is a traditional way of iterating over an object's properties and assigning values to a new object.

**Pros and Cons**

Here are the pros and cons of each approach:

1. **Object.assign()**:
	* Pros:
		+ More concise and expressive syntax.
		+ Less prone to errors due to its safer approach to merging objects.
	* Cons:
		+ May be slower than a traditional `for-in` loop due to the overhead of function calls.
		+ Limited control over the merge process (e.g., no ability to skip certain properties).
2. **For-in loop**:
	* Pros:
		+ More control over the merge process, as you can choose which properties to copy.
		+ Can be faster than `Object.assign()` due to reduced function call overhead.
	* Cons:
		+ Less concise and expressive syntax.
		+ Prone to errors if not used carefully (e.g., checking for property existence before copying).

**Library**

The benchmark does not use any external libraries.

**Special JS features or syntax**

There are no special JavaScript features or syntaxes mentioned in the benchmark definition. However, it's worth noting that `Object.assign()` has been around since ECMAScript 2015 (ES6), while traditional `for-in` loops have been available since early versions of JavaScript.

**Other alternatives**

If you want to explore alternative approaches to merging objects, here are a few options:

1. **Spread operator (`...`)**: This is a newer approach that's gaining popularity, allowing you to merge two objects using the syntax `const result = { ...a, ...b };`.
2. **Object.entries() and Object.fromEntries()**: These methods allow you to iterate over an object's entries and create a new object from them.
3. **Libraries like Lodash or Immutable.js**: These libraries provide additional utility functions for working with objects, including merge functions.

Keep in mind that the choice of approach ultimately depends on your specific use case, performance requirements, and personal preference.

JavaScript Object.assign vs for in loop (version: 0) Benchmark.js

Comparing performance of: `Object.assign vs for in loop`

Created: 5 years ago by: Guest

Go to the latest result

Object.assign

for in loop

Historical Performance Data aggregated from 99 community runs

Desktop Results:

Chrome 70 runs

Firefox 21 runs

Mobile Results:

Chrome 8 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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

JavaScript Object.assign vs for in loop (version: 0) Benchmark.js

Comparing performance of: Object.assign vs for in loop

Created: 5 years ago by: Guest

Go to the latest result

Object.assign

for in loop

Historical Performance Data aggregated from 99 community runs

Desktop Results:

Chrome 70 runs

Firefox 21 runs

Mobile Results:

Chrome 8 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 loop`