The benchmark tests the performance of three different approaches for constructing an object while processing a range of numbers from 0 to 9999 using the reduce method. The methods being compared are:

1. Using the Spread Operator (...)
2. Using Mutation (Directly modifying the accumulator)
3. Using Object.assign()

1. Using the Spread Operator

range(0, 10000).reduce((acc, num) => {
  return {
    ...acc,
    [num]: num
  };
}, {});

• Description: This method utilizes the spread operator to create a new object for every iteration in the reduce function. It expands the contents of the existing acc object (accumulator) into a new object while adding the current number as a key-value pair.

• Pros:

  • Code is concise and expressive, making it easy to read.
  • Functional style that avoids side effects.

• Cons:

  • Can be inefficient as it creates a new object on every iteration, leading to increased memory usage and processing time, especially for large inputs.

2. Using Mutation

range(0, 10000).reduce((acc, num) => {
  acc[num] = num;
  return acc;
}, {});

• Description: This approach directly modifies the acc object by adding new key-value pairs to it.

• Pros:

  • More performant since it mutates the existing object instead of creating a new one, which reduces memory overhead.
  • Better suited for scenarios where performance is critical and when the number of operations (iterations) is large.

• Cons:

  • It has side effects due to directly modifying the accumulator, which might lead to errors if not handled carefully.
  • Less expressive compared to the other methods, which might make it harder for some developers to understand at a glance.

3. Using Object.assign()

range(0, 10000).reduce((acc, num) => {
  return Object.assign(acc, {[num]: num});
}, {});

• Description: This method uses Object.assign() to copy properties from a new object (with the current number as a key) into the accumulator.

• Pros:

  • Offers a clearer intention of merging objects.
  • Avoids some side effects associated with direct mutation as Object.assign can be seen as a non-destructive operation on the surface.

• Cons:

  • Performance-wise, it is generally slower than direct mutation, as it still involves some overhead to create a new object for each iteration.
  • Can be less readable compared to directly mutating the accumulator.

Benchmark Results Summary

The benchmark results show the number of executions per second for each method:

• Mutation is the clear winner with 12,995 executions per second.
• Object.assign() follows with 599 executions per second.
• Spread Operator significantly trails with only 0.44 executions per second.

Other Considerations

• When to use which method: If performance is paramount (e.g., processing a large dataset), opting for mutation is advisable. However, in cases where readability, maintainability, and avoiding side effects are more critical, using the spread operator or Object.assign() might be more suitable.
• Alternatives: Other alternatives could include using libraries like lodash which provides functional utilities for deep merging and cloning objects while considering performance. Moreover, utilizing modern JavaScript features such as Map or Set could also be relevant, depending on the specific requirements of the task (e.g., needing unique keys).

This benchmark illustrates the trade-offs between different JavaScript object construction techniques within a functional programming context, emphasizing the importance of selecting the right method based on use case requirements.