Benchmark: key assignment vs spread operator

Tests:

Spread operator
let obj = {} for(i=0; i<100000; i++){ obj[i] = true } let newObj = { ...obj, foo: 'bar' }
Key assignment
let obj = {} for(i=0; i<100000; i++){ obj[i] = true } obj.foo = 'bar'

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Spread operator
Key assignment

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 11 months ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/137.0.0.0 Safari/537.36 Edg/137.0.0.0

Browser/OS: Chrome 137 on Windows

View result in a separate tab

Test name	Executions per second
Spread operator	305.5 Ops/sec
Key assignment	311.3 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 provided benchmarking test and its results.

**What is being tested?**

The provided JSON represents a JavaScript microbenchmark that tests two different approaches to assign properties to an object:

1. **Key assignment**: This involves assigning a property value directly to an existing object using dot notation (e.g., `obj.foo = 'bar'`).
2. **Spread operator**: This involves creating a new object by spreading an existing object and then adding or overriding specific properties using the spread syntax (e.g., `let newObj = { ...obj, foo: 'bar' }`).

**Options compared**

The benchmark compares these two approaches for assigning properties to an object with 100,000 elements. The test focuses on measuring the performance difference between these two methods.

**Pros and cons of each approach:**

1. **Key assignment (dot notation)**:
	* Pros:
		+ Faster and more efficient, as it directly accesses and modifies the object's property.
		+ Can be useful when working with existing objects that have a specific structure or layout.
	* Cons:
		+ May lead to slower performance for large datasets due to string concatenation and potential property lookup overhead.
2. **Spread operator (object spread)**:
	* Pros:
		+ More intuitive and readable, especially when dealing with complex object assignments or modifications.
		+ Can be useful when working with objects that need to be copied or modified in place.
	* Cons:
		+ May lead to slower performance for large datasets due to the creation of a new object and property assignment.

**Library and syntax considerations**

There is no specific library mentioned in the provided JSON. However, the use of the spread operator (object spread) is a modern JavaScript feature that has been introduced in ECMAScript 2018. It allows creating a shallow copy of an object using the `...` spread operator.

**Other alternatives**

In the past, developers might have used other methods to achieve similar results, such as:

1. **Using `Object.assign()`**: This method copies all enumerable own properties from one or more source objects to a target object.
2. **Using `for...in` loops and property iteration**: These can be used to iterate over an object's properties and assign values manually.

**Benchmark preparation code**

The provided JSON does not include any script preparation code. The test cases are defined directly within the benchmark definition, which is a common approach for simple microbenchmarks.

Overall, this benchmark aims to provide insight into the performance difference between two commonly used methods for assigning properties to objects in JavaScript. By comparing these approaches, developers can make informed decisions about which method is best suited for their specific use cases.

Related benchmarks:

key assignment vs spread operator (version: 0)

Comparing performance of: Spread operator vs Key assignment

Created: 4 years ago by: Guest

Jump to the latest result

Spread operator

Key assignment

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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