The benchmark defined in the JSON snippet titled "Spread vs push(...) for large arrays" focuses on comparing different methods for appending elements to large arrays in JavaScript. Specifically, it evaluates three approaches: using a traditional for loop with the push method, using the concat method, and utilizing the spread operator. Here's a breakdown of each approach, including their pros and cons, and other considerations.

Methods Being Compared

1. Control (for push)

   • Benchmark Definition:

     for (let element of window.test) window.top.tests.control.push(element);
     if (window.top.tests.control.length > window.cutoff) { window.top.tests.control = []; console.log('reset control'); }
     

   • Description: This method iterates through the window.test array using a for...of loop and adds each element to the control array using the push() method.
   • Pros:
     • Simple and straightforward.
     • Efficient for appending individual elements.
   • Cons:
     • May not be the fastest option for a large number of elements due to the repeated calls to push().
     • Generally less concise than other modern approaches.

2. Concat

   • Benchmark Definition:

     window.top.tests.concat = [...window.top.tests.concat, window.test];
     if (window.top.tests.concat.length > window.cutoff) { window.top.tests.concat = []; console.log('reset concat'); }
     

   • Description: This approach uses the spread operator (...) to concatenate the existing concat array with window.test to create a new array.
   • Pros:
     • Clean and expressive syntax.
     • Can effectively handle merging arrays in a single expression.
   • Cons:
     • Creates a new array, resulting in higher memory usage compared to in-place modifications like push().
     • May incur overhead due to array reallocation when the size exceeds the existing capacity.

3. Spread

   • Benchmark Definition:

     window.top.tests.spread.push(...window.test);
     if (window.top.tests.spread.length > window.cutoff) { window.top.tests.spread = []; console.log('reset spread'); }
     

   • Description: This method utilizes the push() function combined with the spread operator to append all elements of window.test to the spread array.
   • Pros:
     • Combines the benefits of push() (in-place modification) with the conciseness of the spread operator.
     • Typically more efficient than concatenating arrays since it allows for appending elements directly.
   • Cons:
     • Still involves a spread operation, which might have some performance hit compared to a simple push() in specific circumstances, although it's generally more performant than using concat().

Benchmarking Results

From the benchmark results, we see the following executions per second for each method:

• Spread: 4,030,276.75
• Control (for push): 913,760.875
• Concat: 548,937.6875

The results clearly demonstrate that the use of the spread operator with push() offers significantly better performance compared to traditional for loops or using concat(). This is particularly beneficial in contexts involving large arrays where performance is a critical concern.

Alternatives

Other alternatives for appending elements to an array in JavaScript could include:

• Array.prototype.unshift() for adding elements to the beginning (less relevant in this benchmark).
• Mutating the array directly using properties or methods from libraries like Lodash or Underscore.js, which can offer additional functionality, though at the cost of additional library weight.
• Utilizing frameworks or libraries that may abstract or optimize array handling based on specific performance characteristics.

Conclusion

In conclusion, this benchmark highlights different methods of appending elements to arrays in JavaScript, revealing the performance benefits of using the spread operator in conjunction with the push() method. Understanding these various techniques can guide engineers in selecting the most efficient and suitable approach for their specific use cases.