Benchmark: .length vs cached length for loop

Tests:

noncached
let k = new Array(1000000).fill(1); let x = 0; for (let i = 0; i < k.length; i++) x++;
cached
let k = new Array(1000000).fill(1); let x = 0, x2 = k.length; for (let i = 0; i < x2; i++) x++;

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
noncached
cached

Fastest: N/A

Slowest: N/A

Latest 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 data and explain what's being tested, compared, and their pros and cons.

**Benchmark Overview**

The benchmark measures the performance difference between two approaches for iterating over an array in JavaScript:

1.  **Non-Cached**: Using the `length` property to determine the number of elements in the array.
2.  **Cached**: Storing the length of the array in a separate variable before the loop.

**Options Being Compared**

The benchmark is comparing these two approaches:

*   **Non-Cached**: This approach uses the `length` property directly within the loop, which can lead to slower performance since it requires multiple read operations.
*   **Cached**: By storing the length of the array in a variable (`x2`) before the loop, this approach avoids repeated reads from the `length` property. Instead, it increments the cached value `x2`, which is more efficient.

**Pros and Cons**

**Non-Cached:**

*   Pros:

*   Simpler code
    *   More straightforward to understand for some developers
*   Cons:

*   More reads from the `length` property can slow down performance

**Cached:**

*   Pros:

*   Fewer read operations from the `length` property, leading to improved performance
    *   Still uses simple and easy-to-understand code
*   Cons:

*   Requires an additional variable for caching, which might be perceived as slightly more complex code

**Library Usage**

There is no explicit library usage mentioned in the provided data. However, the use of `let` and `for` loops implies that JavaScript's built-in features are being leveraged.

**Special JS Feature/Syntax**

There is a special case related to variable hoisting:

*   In JavaScript, variables declared with `let` or `const` are "hoisted" to the top of their scope. This means that even though `x` and `x2` are declared within the loop, they can be accessed before the loop starts due to variable hoisting.

This aspect is not explicitly mentioned in the provided data but affects the interpretation of how variables interact with each other in the benchmarking code.

**Other Alternatives**

Some potential alternatives for optimizing array iteration include:

*   Using `Array.prototype.forEach()` or similar methods, which are designed for performance and can avoid explicit loop logic.
*   Leveraging the optimized `for...of` loops introduced in ECMAScript 2015 (ES6), which provide even better performance than traditional `for` loops.

However, these alternatives might require changes to the code beyond simply swapping between non-cached and cached approaches.

Related benchmarks:

.length vs cached length for loop (version: 0)

Comparing performance of: noncached vs cached

Created: 4 years ago by: Guest

Jump to the latest result

noncached

cached

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):