Benchmark: Array[index] vs local variable

Script Preparation code:

var list = new Array(100000).fill(0);

Tests:

Arra[index]
for (let i = list.length - 1; i >= 0; i--) { if (list[i].a || list[i].b) { const a = list[i].c; } }
Cached with a local variable
for (let i = list.length - 1; i >= 0; i--) { let item = list[i]; if (item.a || item.b) { const a = item.c; } }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Arra[index]
Cached with a local variable

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

**What is being tested?**

The benchmark compares two approaches to accessing elements in an array:

1. **Direct array access**: `list[i].a` or `list[i].b`, where `i` is the index of the element.
2. **Caching with a local variable**: Storing the entire array in a local variable and then using that variable to access elements.

**Options being compared**

The benchmark compares two approaches:

1. **Direct array access**: This approach accesses an element directly from the array, without any additional processing or caching.
2. **Cached with a local variable**: This approach stores the entire array in a local variable and then uses that variable to access elements. This can potentially improve performance by reducing the number of array lookups.

**Pros and cons of each approach**

1. **Direct array access**:
	* Pros: Simple, fast, and efficient for small arrays.
	* Cons: Can be slow for large arrays due to repeated lookups in the array's internal structure.
2. **Cached with a local variable**:
	* Pros: Reduces the number of array lookups, potentially leading to improved performance for large arrays.
	* Cons: Requires more memory to store the entire array, and can lead to slower initialization times.

**Library used**

There doesn't appear to be any specific library being used in this benchmark. The script is using native JavaScript features such as arrays, loops, and object access.

**Special JS feature or syntax**

The benchmark uses a few advanced JavaScript features:

1. **Template literals**: Used in the `const a = list[i].c;` line, which allows for more readable string interpolation.
2. **Array destructuring**: Not explicitly used in this benchmark, but it's a useful feature that can simplify code.

**Other considerations**

When deciding between these two approaches, consider the following factors:

1. **Array size**: For small arrays (e.g., < 100 elements), direct array access is likely sufficient. For larger arrays, caching with a local variable may lead to improved performance.
2. **Performance requirements**: If you need fast and efficient code for large datasets, cached with a local variable might be the better choice.
3. **Memory constraints**: If memory is limited, direct array access may be preferred to avoid unnecessary memory allocation.

**Alternatives**

Other alternatives to consider:

1. **Using `at()` method**: Introduced in ECMAScript 2020, `list.at(i)` allows for more efficient and readable way to access elements at a specific index.
2. **Using `Array.prototype.find()` or `Array.prototype.findIndex()`**: These methods can simplify the logic for accessing elements based on conditions.
3. **Compilers like Webpack or Rollup**: Can optimize and bundle your code, potentially improving performance.

Keep in mind that the best approach will depend on specific use cases and requirements.

Related benchmarks:

Array[index] vs local variable (version: 0)

Comparing performance of: Arra[index] vs Cached with a local variable

Created: 3 years ago by: Guest

Jump to the latest result

Arra[index]

Cached with a local variable

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):