I'd be happy to explain what's being tested in this benchmark.

Benchmark Overview

The benchmark compares the performance of two approaches: nested loops with i as the outer loop and j as the inner loop, versus nested loops with j as the outer loop and i as the inner loop. The loop iterates 10,000 times in each direction.

Script Preparation Code

The script preparation code initializes an empty array arr and populates it with another empty array for each iteration of the outer loop (x). This is done to ensure that the inner loops have access to the correct index values.

Options Compared

There are two main options being compared:

1. Nested Loops with i as Outer Loop and j as Inner Loop
   • Code: for (var i=0; i < 10000; i++) { for (var j=0; j < 10000; j++) { arr[i][j]=i*j; } }
   • This approach is generally considered more efficient because it allows the compiler to optimize the loop bounds and avoid redundant calculations.
2. Nested Loops with j as Outer Loop and i as Inner Loop
   • Code: for (var i=0; i < 10000; i++) { for (var j=0; j < 10000; j++) { arr[j][i]=i*j; } }
   • This approach can be slower because it requires accessing the outer array arr with each inner loop iteration, which can lead to additional memory access and calculations.

Pros and Cons

• Nested Loops with i as Outer Loop:
  • Pros:
    • Often optimized by compilers
    • Can avoid redundant calculations
  • Cons:
    • May not be as intuitive for developers who are not familiar with this structure
• Nested Loops with j as Outer Loop:
  • Pros:
    • Can be more intuitive for developers who are used to this structure
  • Cons:
    • May not be optimized by compilers
    • Can lead to slower performance due to additional memory access and calculations

Other Considerations

• Array Indexing: In both approaches, the inner loops need to calculate the correct index values i*j or j*i. This can add unnecessary complexity and overhead.
• Cache Efficiency: The choice of loop structure can impact cache efficiency. For example, accessing an outer array with each inner loop iteration may lead to more cache misses.

Library Usage

There is no explicit library usage in the benchmark definition. However, the use of JavaScript's built-in for loops and array indexing suggests that the browser's V8 engine (used by Chrome 52) provides the necessary functionality for array manipulation and iteration.

Special JS Features/Syntax

There are no special JavaScript features or syntax used in this benchmark beyond standard loop constructs and array indexing.