Benchmark: For with and without external variables

Script Preparation code:

var arr = [];
for (var i = 0; i < 1000; i++) {
  arr.push({
    Number: i
  });
};

var e = null;
var f = null;

function doWork(o, i) {
  e = o;
};

Tests:

1
var i = 0; var len = arr.length; for (; i <= len; i++) { f = arr[i]; };
2
for (var i = 0, len = arr.length; i <= len; i++) { e = arr[i]; };

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
1
2

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):

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark JSON and explain what's being tested.

**Benchmark Definition**

The benchmark is testing two different approaches to iterating over an array in JavaScript:

1. **For loop with explicit variable scope**: The first test case uses a traditional for loop with explicit variable scope, where `i` is declared as `var i = 0;`. This means that the variable `i` is scoped to the entire block and can be accessed by all statements within.
2. **For loop with early binding**: The second test case uses an older style of for loop, also known as "early binding", where `i` is declared inside the loop condition: `for (var i = 0; i <= len; i++)`. In this case, the variable `i` is bound to the current value of the loop index and can only be accessed within that scope.

**Options compared**

The benchmark is comparing the performance of these two approaches:

* **For loop with explicit variable scope**: This approach allows for more flexibility and can avoid issues related to hoisting in older JavaScript engines.
* **For loop with early binding**: This approach was commonly used before ECMAScript 5, but can lead to issues with scoping and hoisting.

**Pros and Cons**

**Explicit variable scope (for loop)**

Pros:

* More modern and safer approach
* Avoids issues related to hoisting in older JavaScript engines
* Can be more efficient due to better optimization opportunities

Cons:

* May require additional workarounds or transpilation for compatibility with older browsers

**Early binding (for loop)**

Pros:

* Widely supported across different JavaScript engines and versions
* Familiar syntax for many developers

Cons:

* Can lead to issues related to scoping and hoisting, especially in modern JavaScript environments
* May not be optimized as well by some JavaScript engines

**Library: none**

There are no external libraries used in this benchmark.

**Special JS feature or syntax**

Neither of the test cases uses any special JavaScript features or syntax. They only employ standard features of the language.

Now, let's consider alternative approaches:

* **Array.prototype.forEach()**: This method is a modern and efficient way to iterate over arrays in JavaScript. However, it may not be supported by older browsers.
* **For...of loop**: A newer iteration style introduced in ECMAScript 2015 (ES6). It provides a more concise and expressive way to iterate over arrays, but may not be widely supported across different browsers.

Note that the benchmark is focused on comparing two specific approaches and does not cover other aspects of array iteration or JavaScript performance.

Related benchmarks:

For with and without external variables (version: 0)

Comparing performance of: 1 vs 2

Created: 8 years ago by: Guest

Jump to the latest result

1

2

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):