This benchmark tests the performance of two different methods for filtering even numbers from an array in JavaScript:

Method 1: New Array with Spread (...) Operator:

const testData = [...Array(100000).keys()]; // Creates an array of 100,000 numbers from 0 to 99,999
const evens = testData.reduce((acc, v) => {
  if (v % 2 === 0) {
    acc = [...acc, v]; // Create a new array with the current value if it's even
  }
  return acc;
}, []); // Start with an empty accumulator array

console.log(evens.length);

Method 2: Accumulator push() Method:

const testData = [...Array(100000).keys()];
const evens = testData.reduce((acc, v) => {
  if (v % 2 === 0) {
    acc.push(v); // Add the current value to the accumulator array if it's even
  }
  return acc;
}, []);

console.log(evens.length);

Pros and Cons:

• Method 1 (Spread Operator):

  • Pro: Potentially more readable for some developers due to its explicit creation of new arrays.
  • Con: Creating a new array in every iteration can be memory-intensive, especially with large datasets.

• Method 2 (Accumulator push()):

  • Pro: More efficient in terms of memory usage as it modifies the existing accumulator array.
  • Con: Can be less readable for some developers compared to Method 1's explicit array creation.

Other Considerations:

• Data Size: For smaller datasets, the performance difference between the two methods might be negligible. The impact becomes more noticeable with larger arrays due to memory allocation overhead.
• Profiling Tools: Use profiling tools like Chrome DevTools to analyze the actual execution time and memory usage of each method for your specific use case and data size.

Alternatives:

• Filtering using Array Methods: You could use filter() directly instead of reduce(), which might be more performant:

  const evens = testData.filter(v => v % 2 === 0); 
  

Let me know if you have any other questions!