Benchmark: loop length recalculation

Script Preparation code:

  var arr=new Array(1000000).fill(0)

Tests:

normal loop
for (var i=0;i<arr.length;i++){val=arr[i]}
loop without length
var l=arr.length; for (var i=0;i<l;i++){val=arr[i]}
reverse loop
for (var i=arr.length;i>0;i--){val=arr[i]}
weird trick
for (var i=arr.length;i>0;i--){val=arr[i]|0}

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
normal loop
loop without length
reverse loop
weird trick

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 27 days ago):

LLMs can make mistakes. Check important info.

Measuring JavaScript performance is crucial in modern web development. Let's dive into the provided benchmark.

**Benchmark Definition**

The benchmark definition represents a JavaScript code snippet that defines how to test the performance of a loop. There are four variations:

1. **Normal Loop**: A traditional `for` loop where the index variable `i` is incremented.
2. **Loop without Length**: A variation where the length of the array is stored in a separate variable `l` and used for looping instead of accessing the array's `length` property directly.
3. **Reverse Loop**: A loop that iterates from the end of the array to the beginning, decrementing the index variable `i`.
4. **Weird Trick**: An unusual approach that uses bitwise OR operation (`|0`) on the value retrieved from the array.

**Comparison Options**

The benchmark compares the performance of these four loop variations:

* **Pros and Cons:**
	+ **Normal Loop**: This is a traditional way to iterate over an array in JavaScript. It's easy to read and maintain, but it might be slower due to the overhead of accessing the `length` property.
	+ **Loop without Length**: By storing the length in a separate variable, this approach avoids accessing the `length` property, which can be faster. However, it requires an additional memory allocation and access to store the length value.
	+ **Reverse Loop**: This loop iterates from the end of the array, which can be slower due to the need to decrement the index variable. Additionally, it may not work correctly if the array is already sorted or has duplicate values.
	+ **Weird Trick**: Using bitwise OR operation (`|0`) on the value retrieved from the array is a non-standard approach that might not work as expected in all browsers or environments. It's unlikely to be faster than the other options and may even cause performance issues due to its unusual behavior.
* **Other Considerations:**
	+ The `for` loop with incrementing index variable (`i`) is generally the fastest way to iterate over an array in JavaScript.
	+ Using a separate variable for the length (as in "Loop without Length") can be beneficial if the array size needs to be stored and reused.

**Library or Special JS Feature**

None of the provided test cases use any libraries or special JavaScript features. The focus is solely on comparing the performance of different loop variations.

**Test User Special JS Feature or Syntax**

There are no special JavaScript features or syntax used in these test cases.

Now, let's look at the latest benchmark results:

The results show that the normal loop (without the length stored) performs the fastest, followed closely by the "Loop without Length" variation. The reverse loop and weird trick variations perform significantly slower.

**Alternatives**

Some alternative approaches to measuring JavaScript performance include:

1. **Benchmarking libraries:** Libraries like Benchmark.js or jsperf provide a more comprehensive way to measure performance, allowing for the measurement of multiple functions, loops, and even specific lines of code.
2. **V8 Profiling API:** The V8 Profiling API provides detailed profiling information about JavaScript engine execution, including timing, heap allocation, and CPU usage.
3. **Modern testing frameworks:** Testing frameworks like Jest or Mocha provide built-in support for performance testing, making it easier to write and run benchmarks.

In conclusion, the benchmark definition provided outlines a straightforward way to measure the performance of different loop variations in JavaScript. By understanding the pros and cons of each approach, developers can make informed decisions about which loop variation to use in their own code.

Latest run results:

Run details: (Test run date: 7 years ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/52.0.2743.116 Safari/537.36 Edge/15.15063

Browser/OS: Chrome 52 on Windows

View result in a separate tab

Test name	Executions per second
normal loop	3.9 Ops/sec
loop without length	4.9 Ops/sec
reverse loop	4.9 Ops/sec
weird trick	4.4 Ops/sec

Related benchmarks:

loop length recalculation (version: 0)

Comparing performance of: normal loop vs loop without length vs reverse loop vs weird trick

Created: 7 years ago by: Guest

Jump to the latest result

normal loop

loop without length

reverse loop

weird trick

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 27 days ago):