Benchmark Overview

The benchmark titled "Spread vs Object.assign (mutation)" compares the performance of two different methods for merging JavaScript objects: using Object.assign and using the spread operator (...). It evaluates how both methods perform when merging a varying number of objects (from two to six), focusing on execution speed.

Options Compared

The two primary methods being compared in this benchmark are:

1. Object.assign:

   • Examples in Benchmark:
     • const object7 = Object.assign(object1, object2);
     • const object7 = Object.assign(object1, object2, object3);
     • and so forth, up to six objects.

2. Spread Operator (...):

   • Examples in Benchmark:
     • const object7 = {...object1, ...object2};
     • const object7 = {...object1, ...object2, ...object3};
     • and so forth, up to six objects.

Pros and Cons

Object.assign

• Pros:

  • Explicitly designed for merging objects, which may improve readability in certain cases.
  • Can mutate the target object in the first argument, allowing for in-place updates.

• Cons:

  • Mutates the first object passed in as an argument, which can lead to unintended side effects if not handled carefully.
  • Typically slower than the spread operator, as observed in the benchmark results.

Spread Operator (...)

• Pros:

  • Does not mutate the original objects, producing a new object instead, which is safer for functional programming paradigms.
  • Tends to be more concise and often considered more readable.
  • In modern JavaScript engines, frequently optimized for performance, making it faster, especially in scenarios with multiple objects.

• Cons:

  • Slightly less explicit regarding its intention to merge multiple objects compared to Object.assign.

Results Analysis

The benchmark results show significant variances in execution speed between the two methods. The results reveal that:

• Object.assign outperforms the spread operator when merging two and three objects, but this trend shifts as more objects are included.
• By the time six objects are involved, the spread operator exhibits superior performance than Object.assign.

Other Considerations

1. Readability and Maintainability: While the performance is important, the choice between Object.assign and the spread operator should also consider code readability and maintainability. The spread operator is often seen as cleaner and more expressive.

2. Modern JavaScript Engines: The benchmark results can vary between different JavaScript engines (V8, SpiderMonkey, JavaScriptCore, etc.). Performance optimizations may change, affecting which method is faster over time.

3. Mutability and Side Effects: Given that Object.assign mutates the target object, developers should be cautious when using it in contexts where immutability is desired.

Alternatives

In addition to the two methods compared in the benchmark, alternatives for merging objects include:

• Lodash's _.merge(): Lodash offers a robust utility library that includes deep merging of objects. However, it comes with a larger footprint and may not offer performance benefits compared to native approaches.

• Using Object.entries() and Array.prototype.reduce(): One could merge objects using functional approaches, but these are often less performant for simple merging tasks compared to the tested methods.

Conclusion

This benchmark acts as a practical exploration of the performance characteristics of object merging techniques in JavaScript. It highlights the evolving standards and best practices in the language, as developers often need to balance performance with code clarity and functionality.