Benchmark Overview

This benchmark is designed to evaluate the performance of various methods for initializing an array in JavaScript using a mapping function. The filler function takes an index and returns the square of that index, simulating a typical computation during the array initialization process.

Tested Approaches

Five individual test cases compare different methods for array initialization and mapping:

1. Spread Operator with Array Keys

   • Code: [...Array(n).keys()].map(filler);
   • This approach creates an array of the indices from 0 to n-1 using the spread operator and Array.keys(), then applies the filler function to each index.
   • Pros: This method is concise and utilizes modern JavaScript features.
   • Cons: It can hit the maximum call stack size when using large n values, potentially leading to inefficiency.

2. Array.apply with Map

   • Code: Array.apply(null, { length: n }).map(filler);
   • This utilizes the Function.prototype.apply method to create an empty array with a specific length, and then maps over it with the filler function.
   • Pros: Creates a sparse array for mapping without intermediate steps.
   • Cons: This approach is less common and may not be as performant depending on the JavaScript engine's handling of apply.

3. Array.from Method

   • Code: Array.from({ length: n }, filler);
   • Array.from can create a new array and apply the filler function to each element. It generates the indices automatically.
   • Pros: This is a standardized method that is widely supported and understood. It avoids issues related to the call stack.
   • Cons: Introduces some overhead because it has to set up a new structure for the array.

4. Filling an Array with Undefined and Mapping

   • Code: Array(n).fill(undefined).map(filler);
   • This approach first fills a new array with undefined values and then maps over the array with the filler function.
   • Pros: Straightforward to understand and avoids maximum call stack issues.
   • Cons: This creates an intermediate array filled with undefined, which may have unnecessary memory overhead.

5. Classic For Loop

   • Code:

   const arr = [];
   for (let i = 0; i < n; i++) {
     arr.push(filler(null, i));
   }
   

   • This traditional approach manually builds the array by pushing calculated values into it.
   • Pros: It often provides the best performance for large arrays because it avoids the overhead of higher-order functions.
   • Cons: While clear and effective, this approach can result in more boilerplate code compared to functional methods.

Benchmark Results

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

• For Loop Push: 2903.73 executions/sec (fastest)
• Array.from: 999.24 executions/sec
• Array(n).fill(undefined).map(filler: 755.93 executions/sec
• Spread Operator: 622.73 executions/sec
• Array.apply: 398.89 executions/sec (slowest)

Considerations

When selecting an array initialization approach in JavaScript, several factors come into play:

• Performance: The classic for loop demonstrates the best performance in this benchmark, particularly for larger arrays.
• Readability: Higher-order functions like map and Array.from can make code clearer and more expressive, which is beneficial for team collaboration.
• Stack Size: Approaches using the spread operator with large n could lead to stack overflow errors and thus are less reliable.
• Browser Compatibility: All methods are compatible across modern environments, but specific features like Array.from may not be supported in older JavaScript engines.

Alternatives

Other alternatives for array initialization might include using Array.fill, Unshift/Concat, or even employing libraries like Lodash, which provide utility methods for more advanced data manipulation patterns. Each of these methods balances performance and readability differently, and the best choice may depend on the specific use case and context in which you are working.