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Array loops
(version: 1)
Comparing performance of:
for vs reverse while vs caching while
Created:
9 years ago
by:
Registered User
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Script Preparation code:
function noop() {} var array = []; (function () { var length = 100; while (length--) { array.push(Math.random()); } })();
Tests:
for
var i = 0; var length = array.length; for (; i < length; i++) { noop(array[i]); }
reverse while
var i = array.length; while (i--) { noop(array[i]); }
caching while
var i = 0; var item; while (item = array[i++]) { noop(item); }
Rendered benchmark preparation results:
Suite status:
<idle, ready to run>
Run tests (3)
Previous results
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Test case name
Result
for
reverse while
caching while
Fastest:
N/A
Slowest:
N/A
Latest run results:
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Autogenerated LLM Summary
(model
llama3.2:3b
, generated one year ago):
I'll break down the provided benchmark definition and explain what's being tested, compared options, pros and cons of those approaches, library usage, special JavaScript features or syntax, and other considerations. **Benchmark Definition** The benchmark measures performance differences between three loop constructs in JavaScript: 1. **`for` loop**: Iterates over an array using a traditional `for` loop with an index variable. 2. **`reverse while` loop**: Iterates over an array using a `while` loop, where the condition is inverted, and the index variable increments. 3. **`caching while` loop**: Iterates over an array using a `while` loop with caching of the current element. **Loop Comparison Options** These loops have different performance characteristics: * **`for` loop**: Typically provides good cache locality because it iterates over the elements in a sequential manner. * **`reverse while` loop**: Has poor cache locality due to the inverted condition, which can lead to slower performance. * **`caching while` loop**: Offers better cache locality compared to `reverse while` but still not as good as the traditional `for` loop. **Pros and Cons of Each Approach** * **`for` loop**: * Pros: Good cache locality, predictable iteration order * Cons: Less flexible than other loops * **`reverse while` loop**: * Pros: None notable * Cons: Poor cache locality, inverted condition can lead to slower performance * **`caching while` loop**: * Pros: Better cache locality than `reverse while`, still sequential iteration order * Cons: Less predictable iteration order compared to traditional `for` **Library Usage** None. **Special JavaScript Features or Syntax** None mentioned in the benchmark definition. However, it's worth noting that some modern JavaScript engines like V8 (used by Google Chrome) and SpiderMonkey (used by Firefox) use various micro-optimizations that can affect performance in loops. **Other Considerations** * The benchmark uses a fixed array size of 100 elements. * The `noop` function is used to measure the time taken for each loop, which means it's not actually performing any meaningful operation. This is done to isolate the loop iteration overhead. * The benchmark runs on multiple devices and browsers, providing a broader perspective on performance differences. **Alternatives** There are other alternatives for comparing loop performance in JavaScript: * **`while (true)` loop**: Similar to `for` loops but doesn't provide cache locality. However, it can be modified to use caching. * **`forEach()` method**: This is a built-in array method that iterates over an array using a closure. It provides better cache locality than traditional loops and is often faster in modern JavaScript engines. These alternatives offer different performance characteristics and trade-offs, which may affect the results of benchmarking loop performance.
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