The benchmark described compares three different methods of combining arrays in JavaScript: the traditional Array.prototype.concat method, the ES6 spread operator, and the Array.prototype.push method with the spread operator used to spread elements into the array. The goal is to assess the performance differences between these approaches when adding a large array (1,000 elements) to a smaller one (100 elements).

Comparison of Options:

1. Array.prototype.concat

   • Benchmark Definition:

     var params = Array(1000);
     var array = Array(100);
     var other = array.concat(params);
     

   • Pros:
     • Straightforward and easy to understand.
     • Does not mutate the original arrays; it returns a new array.
   • Cons:
     • Historically, it can be slower compared to modern approaches, especially as arrays grow larger.
   • Performance Result: 1,548,080.5 executions per second.

2. Spread Operator ([...])

   • Benchmark Definition:

     var params = Array(1000);
     var array = Array(100);
     var other = [...array, ...params];
     

   • Pros:
     • Very readable and concise syntax for combining arrays.
     • Like concat, it does not modify the original arrays; it creates a new array.
   • Cons:
     • In certain cases and engines, performance can be less optimal compared to concat, especially with very large datasets.
   • Performance Result: 247,534.33 executions per second.

3. Push Method (push(...params))

   • Benchmark Definition:

     var params = Array(1000);
     var array = Array(100);
     var other = array.push(...params);
     

   • Pros:
     • The push method modifies the existing array, potentially making it faster in terms of memory operations.
     • It can be more efficient since it adds elements directly to the original array.
   • Cons:
     • This method mutates the original array, which can lead to unintended side effects if the original array is expected to remain unchanged.
   • Performance Result: 460,680.06 executions per second.

Summary of Results:

• Fastest Method: Array.prototype.concat was the fastest option in this benchmark, achieving over 1.5 million executions per second.
• Push came in second, performing significantly slower than concat but faster than the spread operator.
• Spread Operator was the slowest option among the three. Although it provides cleaner syntax, its performance can lag behind both concat and push.

Other Considerations:

• Readability vs. Performance: While concat is currently the fastest method, the readability of the spread operator may make it preferable in many codebases, especially for smaller arrays. For larger arrays and performance-critical applications, concat could be the better choice.
• Mutability: Using push alters the original array, which is crucial to consider in functional programming paradigms where immutability is often preferred.

Alternatives:

• For Loops: Developers can manually combine arrays using for loops, which allows for full control of the merging logic but often sacrifices readability and may introduce performance issues unless optimized.
• Array.from(): Another approach is to use Array.from() in conjunction with methods like map() to transform and combine arrays, although this approach typically lacks the performance benefits of the above methods.
• Libraries: Libraries like Lodash can provide utility functions for merging arrays with additional features, but they add overhead in terms of package size and dependency management.

In conclusion, when selecting a method for combining arrays, developers should balance performance, readability, and mutability based on the needs of their specific application or context.