What is being tested?

MeasureThat.net is testing the performance of two approaches to merge objects in JavaScript:

1. Spread Operator (...): This syntax allows you to expand an object's properties into another object.
2. Object.assign(): This method copies all enumerable own properties from one or more source objects to a target object.

The benchmark compares the performance of these two approaches when merging two objects without mutating the original objects.

Options being compared

• Using the spread operator (...) for object merging
• Using Object.assign() for object merging

Pros and Cons of each approach:

Using the Spread Operator (...)

Pros:

• More concise and readable code
• No need to specify the target object or existing properties
• Efficient in modern JavaScript engines

Cons:

• Requires support for modern JavaScript features (introduced in ECMAScript 2018)
• May not work as expected if the source objects have non-enumerable properties

Using Object.assign()

Pros:

• Widespread support across older browsers and versions of Node.js
• Can handle non-enumerable properties more accurately than the spread operator
• Works with any JavaScript engine, including older ones

Cons:

• Less concise and readable code compared to the spread operator
• Requires specifying the target object or existing properties

Other considerations

• Library usage: There is no library mentioned in the benchmark definition. However, Object.assign() has been a built-in method of the global Object since ECMAScript 5 (2009), so it doesn't require any external libraries.

Special JS feature or syntax

None are explicitly mentioned in this benchmark. However, the spread operator (...) was introduced in ECMAScript 2018 and might not work correctly in older JavaScript engines.

Other alternatives

If you prefer a different approach to object merging, here are some alternative methods:

• Object.create(): This method creates a new object with the given prototype. You can then assign properties to it using Object.assign() or other means.
• JSON merge algorithms: There are various JSON merge algorithms available, such as Lodash's merge() function or a custom implementation.

Keep in mind that these alternatives might have different performance characteristics compared to the spread operator and Object.assign().