The benchmark titled "Object.assign vs destructuring again" aims to compare two JavaScript approaches for merging objects and adding new properties: using Object.assign() and the spread syntax (...).

Approaches Being Compared

1. Object.assign

   • Benchmark Definition:

     const res = Object.assign(obj, { toString: function() { return this.one; }});
     

   • Test Name: "Object.assign"
   • Description:
     • Object.assign() is a built-in method that copies the values of all enumerable own properties from one or more source objects to a target object. In this case, it takes an existing object obj and adds a new property toString to it, which is a function that returns the value of this.one.

2. Destructuring (with spread)

   • Benchmark Definition:

     const res = {...obj, toString: function() { return this.one; }};
     

   • Test Name: "Destructuring"
   • Description:
     • The spread syntax (...) allows an iterable (like an object) to be expanded in places where zero or more elements are expected. This syntax creates a new object, incorporating all properties from obj and adding a new toString function.

Pros and Cons

Object.assign

• Pros:

  • Directly modifies the target object, which might be desirable in certain scenarios.
  • Simplicity in terms of syntax for copying properties.

• Cons:

  • Can lead to mutation of the original object if not used carefully (since it's modifying obj directly).
  • Less efficient in terms of performance when merging multiple objects due to its nature of performing more operations.

Destructuring (Spread Syntax)

• Pros:

  • Creates a new object, which is a more functional programming approach that avoids side effects and mutations to existing objects.
  • Generally more concise and easier to read, especially for combining multiple objects.

• Cons:

  • Can be slightly less performant compared to Object.assign() in specific cases, as it creates a new object rather than modifying an existing one.
  • When dealing with very large objects or when merging many objects, the performance cost can be higher due to the copy.

Benchmark Results

• The benchmark results show that Object.assign resulted in 21,209,232 executions per second, while the destructuring approach had 13,726,364 executions per second in Firefox. This indicates that, at least in this context and environment, Object.assign was significantly faster.

Other Considerations

• Performance may vary across different browsers and environments. The benchmark was conducted on Firefox 136 on macOS, so results might differ when tested in other browsers or platforms.
• Similar benchmarks in other contexts might yield different results based on the size of the objects being merged, the number of properties, and the overall complexity of the added functions.

Alternatives

Other alternatives for merging or combining objects in JavaScript include:

• Using Object.entries() / Object.fromEntries(): It can be used to merge key-value pairs with more control, but involves more steps.
• Lodash's _.merge(): A utility library that can deeply merge objects but may introduce additional overhead.
• ES6 classes with inheritance: For scenarios where behavior and structure are essential, creating a class might be better suited than object merging.

This benchmark provides a practical insight into the performance trade-offs between two common methodologies for object merging in JavaScript.