Benchmark: JavaScript Object.assign vs for in loop new

Tests:

Object.assign
const a = { A: 'a', B: 'b', C: 'c', D: 'd', E: 'e', F: 'f', G: 'g', H: 'h', I: 'i', J: 'j', K: 'k', L: 'l', M: 'm', } const b = { A: 'n', B: 'o', C: 'p', D: 'q', E: 'r', F: 's', G: 't', H: 'u', I: 'v', J: 'w', K: 'x', L: 'y', M: 'z', } Object.assign(a, b);
for in loop
const a = { A: 'a', B: 'b', C: 'c', D: 'd', E: 'e', F: 'f', G: 'g', H: 'h', I: 'i', J: 'j', K: 'k', L: 'l', M: 'm', } const b = { A: 'n', B: 'o', C: 'p', D: 'q', E: 'r', F: 's', G: 't', H: 'u', I: 'v', J: 'w', K: 'x', L: 'y', M: 'z', } for (let prop in b) a[prop] = b[prop];

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: one year ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/113.0.0.0 Safari/537.36

Browser/OS: Chrome 113 on Windows

View result in a separate tab

Test name	Executions per second
Object.assign	3378279.0 Ops/sec
for in loop	5165994.0 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down the benchmark and explain what's being tested, compared, and their pros and cons.

**Benchmark Definition**

The benchmark is testing two approaches to merge two objects in JavaScript: `Object.assign` and a for-in loop with object assignment.

**Options Compared**

1. **Object.assign**: This method takes two or more objects as arguments and merges them into the first object.
2. **For-in loop with object assignment**: This approach uses a for-in loop to iterate over the properties of one object (in this case, `b`) and assigns each property value to the corresponding key in another object (`a`).

**Pros and Cons**

1. **Object.assign**
	* Pros:
		+ Shorter and more concise code.
		+ Often considered more readable.
		+ Less prone to errors, as it handles missing properties automatically.
	* Cons:
		+ May be slower due to the overhead of function calls.
		+ May not work correctly if the source object is not an object (e.g., a plain JavaScript object).
2. **For-in loop with object assignment**
	* Pros:
		+ Can be faster, as it avoids the overhead of function calls and uses direct property access.
		+ More control over the merging process, as each iteration can be customized.
	* Cons:
		+ Longer and more verbose code.
		+ May lead to errors if not implemented correctly.

**Library/Features Used**

In this benchmark, there is no explicit library or feature used. The focus is on comparing two different approaches to merge objects in JavaScript.

**Special JS Features/Syntax**

None mentioned in the provided JSON.

**Other Alternatives**

If you want to test other approaches to merge objects, here are a few alternatives:

1. Using `Array.prototype.reduce()`: This method can be used to merge objects by reducing an array of key-value pairs into the target object.
2. Using `Object.keys()` and `forEach()`: This approach involves iterating over the keys of one object using `Object.keys()` and assigning each value to the corresponding key in another object using a callback function with `forEach()`.
3. Using destructuring assignment: This method involves using destructuring assignment to extract properties from two objects and assign them to new variables.

Keep in mind that these alternatives may have different performance characteristics, code readability, and error handling compared to `Object.assign` and the for-in loop approach.

Related benchmarks:

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

Comparing performance of: Object.assign vs for in loop

Created: one year ago by: Guest

Jump to the latest result

Object.assign

for in loop

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

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