Benchmark: Caching length property vs getting it each time in the loop vs other loops

Script Preparation code:

var arr = [];
var count = 1000;
for(var i = 0; i<count; i++)
{
  arr.push(i);
}

Tests:

Cache length
var arrLen = arr.length; var sum = 0; for (var i = 0; i < arrLen; i++){ sum = arr[i]; }
Do not cache
var sum = 0; for (var i = 0; i < arr.length; i++){ sum = arr[i]; }
for let
var sum = 0; for (let i of arr) { sum = i; }
for var
var sum = 0; for (var i of arr) { sum = i; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Cache length
Do not cache
for let
for var

Fastest: N/A

Slowest: N/A

Latest run results:

No previous run results

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Autogenerated LLM Summary (model llama3.2:3b, generated one year ago):

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Let's break down the provided JSON and explain what is tested, compared options, pros and cons of those approaches, and other considerations.

**Benchmark Definition**

The benchmark definition is a set of instructions that defines how to prepare the JavaScript environment for testing. In this case:

* The script preparation code creates an array `arr` with 1000 elements and pushes values from 0 to 999 onto it.
* There are three different test cases:
	+ "Cache length": saves the length of the array in a variable and uses it instead of getting the length each time.
	+ "Do not cache": doesn't use any caching mechanism.
	+ "for let" and "for var": two alternative loop syntaxes.

**Options Compared**

The three test cases compare different approaches:

1. **Cache length**: This approach saves the length of the array in a variable `arrLen` and uses it to loop through the array, instead of getting the length each time using `arr.length`. This can potentially improve performance by avoiding the overhead of the `length` property access.
2. **Do not cache**: This is the baseline approach that doesn't use any caching mechanism.
3. **for let** and **for var**: These two test cases compare different loop syntaxes. The "for let" syntax is a modern JavaScript feature introduced in ECMAScript 2015, while "for var" is an older syntax.

**Pros and Cons**

Here are the pros and cons of each approach:

1. **Cache length**:
	* Pros: Can potentially improve performance by avoiding the overhead of `length` property access.
	* Cons: May not work as expected in certain scenarios (e.g., if the array is modified while looping).
2. **Do not cache**:
	* Pros: Simple and straightforward, no potential issues with caching.
	* Cons: May perform slower due to repeated `length` property accesses.
3. **for let** and **for var**:
	* **For let**: A modern JavaScript feature that allows for more expressive loop syntaxes.
	* Pros: Can improve code readability and maintainability.
	* Cons: May not be supported in older browsers or versions of JavaScript.
	* **For var**: An older syntax that is still widely used but less readable than "for let".
	Pros: Still widely supported, easy to understand for those familiar with the syntax.
	Cons: Less expressive than "for let" and may lead to more verbose code.

**Other Considerations**

1. **Library usage**: There are no libraries mentioned in the benchmark definition. However, if a library is used in one of the test cases, it's essential to consider its impact on performance and accuracy.
2. **Special JS features or syntax**: The "for let" and "for var" test cases utilize specific JavaScript features. Understanding how these features work and their implications on performance can help interpret the benchmark results.

**Alternatives**

If you wanted to compare different approaches, here are some alternative options:

1. **Use a different caching mechanism**: Instead of using the `length` property access, consider using other caching mechanisms like storing the length in a global variable or an object.
2. **Compare with different loop algorithms**: Consider comparing the performance of different loop algorithms, such as a linear search vs. a binary search.
3. **Add more test cases**: Add more test cases to compare different aspects of the JavaScript engine, such as string manipulation, array methods, or object creation.

By understanding these factors and considering alternative approaches, you can gain a deeper insight into how the JavaScript engine works and what optimizations can be applied to improve performance.

Related benchmarks:

Caching length property vs getting it each time in the loop vs other loops (version: 0)

save length of the array in the variable vs get it the loop

Comparing performance of: Cache length vs Do not cache vs for let vs for var

Created: 5 years ago by: Guest

Jump to the latest result

Cache length

Do not cache

for let

for var

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

No previous run results

Autogenerated LLM Summary (model llama3.2:3b, generated one year ago):