Benchmark: index array vs cache indexed value

Script Preparation code:

var arr = [];
for(let i = 0; i < 10000; i++) {
  arr.push(Math.random());
}
var arrLength = arr.length;

Tests:

cached indexed value
let sum = 0; for(let i = 0; i < arrLength; i++) { const el = arr[i]; sum += el; sum += el; sum += el; sum += el; sum += el; }
index each iteration
let sum = 0; for(let i = 0; i < arrLength; i++) { sum += arr[i]; sum += arr[i]; sum += arr[i]; sum += arr[i]; sum += arr[i]; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
cached indexed value
index each iteration

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: one month ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/133.0.0.0 Safari/537.36 Edg/133.0.0.0

Browser/OS: Chrome 133 on Windows

View result in a separate tab

Test name	Executions per second
cached indexed value	14675.0 Ops/sec
index each iteration	7606.6 Ops/sec

Autogenerated LLM Summary (model gpt-4o-mini, generated one month ago):

LLMs can make mistakes. Check important info.

The benchmark you provided tests two different approaches to indexing an array in JavaScript: caching the indexed value and accessing the array directly in a loop. Here’s a breakdown of the tests, the underlying concepts, and the comparisons they entail.

### Comparison of Approaches

1. **Cached Indexed Value**
   - **Benchmark Definition**: 
     ```javascript
     let sum = 0;
     for(let i = 0; i < arrLength; i++) {
         const el = arr[i];
         sum += el;
         sum += el;
         sum += el;
         sum += el;
         sum += el;
     }
     ```
   - **What it Does**: This test caches the value of `arr[i]` into the variable `el` before entering the repetitive addition. Each iteration uses the cached value rather than accessing the array multiple times.
   - **Pros**:
     - Accessing a variable (like `el`) is generally faster than accessing an array element repeatedly due to reduced lookups.
     - This approach may improve readability by emphasizing the intention of the code.
   - **Cons**:
     - If the size of the array (`arrLength`) is small, the performance difference may be negligible, as the overhead of caching might not be justified.
   
2. **Index Each Iteration**
   - **Benchmark Definition**: 
     ```javascript
     let sum = 0;
     for(let i = 0; i < arrLength; i++) {
         sum += arr[i];
         sum += arr[i];
         sum += arr[i];
         sum += arr[i];
         sum += arr[i];
     }
     ```
   - **What it Does**: This test accesses the array directly during each addition, meaning that for every iteration, the array is accessed multiple times for the same index.
   - **Pros**:
     - The code remains simple and straightforward as it directly accesses the array without any intermediate variables.
   - **Cons**:
     - Multiple accesses to the array in the loop can add overhead due to index lookups. This can lead to slower performance compared to the cached approach, particularly in larger arrays or more complex data structures.

### Benchmark Results

- **Cached Indexed Value**: `14675.04` executions per second
- **Index Each Iteration**: `7606.61` executions per second

In this benchmark, the cached indexed value approach outperforms the regular index access by a significant margin. This clearly illustrates that indexing optimization can lead to notable performance gains in JavaScript.

### Other Considerations

- **Memory Usage**: While caching values can improve speed, it may increase memory usage, especially if the loop deals with large data structures or where many variables are cached.
- **Compiler Optimizations**: Modern JavaScript engines (like V8 used in Chrome) are highly optimized and can perform certain optimizations under the hood, but they cannot always predict the best optimization strategy when it comes to repeated access patterns.

### Alternatives

1. **Using `forEach`**:
   - Instead of traditional indexing loops, methods like `array.forEach(function(el) { })` can be used. However, this introduces overhead as it creates function contexts for each element and may result in slower performance.

2. **for...of Loop**:
   - JavaScript's `for...of` syntax provides an easy way to iterate over iterable collections, including arrays. While it often enhances readability, performance can vary based on implementation.

3. **Using libraries**:
   - Libraries like Lodash or Underscore.js can help with data manipulation but may introduce performance overhead due to abstraction.

### Conclusion

In summary, the benchmark effectively illustrates the performance implications of accessing array values directly compared to caching them. For developers, employing caching strategies can lead to more efficient code, especially in scenarios involving large datasets or computationally intensive tasks. As always, performance should be considered in the context of the specific application and workload, and benchmarks like these can help in making informed decisions.

Related benchmarks:

index array vs cache indexed value (version: 1)

Comparing performance of: cached indexed value vs index each iteration

Created: one month ago by: Guest

Jump to the latest result

cached indexed value

index each iteration

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model gpt-4o-mini, generated one month ago):