Benchmark: for vs for with var len

Script Preparation code:

var array = new Array(1000);

Tests:

for a
for (var i = 0; i < array.length; i++) { array[i]; }
for b
var len = array.length; for (var i = 0; i < len; i++) { array[i]; }
for c
for (var i = 0; i < 1000; i++) { array[i]; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
for a
for b
for c

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: one year ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/111.0.0.0 Safari/537.36 OPR/97.0.0.0

Browser/OS: Opera 97 on Windows

View result in a separate tab

Test name	Executions per second
for a	6712.8 Ops/sec
for b	12717.4 Ops/sec
for c	13271.1 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's dive into the explanation of what's being tested on the provided JSON.

**Benchmark Overview**

The benchmark is designed to compare the performance of three different loop structures in JavaScript:

1. Traditional `for` loop with automatic variable declaration (`var i = 0;`)
2. `for` loop with explicit variable declaration and assignment (`var len = array.length; for (var i = 0; i < len; i++)`)
3. Simple `for` loop without variables (`for (var i = 0; i < 1000; i++)`)

**Options Compared**

The three loops are compared in terms of their execution speed, measured by the number of executions per second.

**Pros and Cons of Each Approach**

1. **Traditional `for` loop with automatic variable declaration (`var i = 0;`)**:
	* Pros: Easy to write, familiar syntax.
	* Cons: May lead to slower performance due to the overhead of automatic variable creation and garbage collection.
2. **`for` loop with explicit variable declaration and assignment (`var len = array.length; for (var i = 0; i < len; i++)`)**:
	* Pros: Can be faster, as the variable is declared only once and can be reused.
	* Cons: May lead to errors if the `len` variable is not updated correctly. Requires manual management of scope.
3. **Simple `for` loop without variables (`for (var i = 0; i < 1000; i++)`)**:
	* Pros: Typically faster, as it eliminates the overhead of automatic variable creation and garbage collection.
	* Cons: May be less readable due to the lack of explicit variable declarations.

**Library Usage**

There is no library explicitly mentioned in the provided JSON. However, if we assume that `array` is an array data structure from the JavaScript standard library (e.g., `Array.prototype`), then the `length` property is a built-in property of arrays.

**Special JS Features or Syntax**

None are explicitly used in this benchmark.

**Other Alternatives**

Other alternatives to consider for loop performance comparisons might include:

* `while` loops
* Array methods like `map()`, `forEach()`, and `reduce()` (which can provide better performance for certain use cases)
* Async loops, which can be useful for I/O-bound operations

Keep in mind that the choice of loop structure depends on the specific requirements and constraints of the problem being solved.

In general, the traditional `for` loop with automatic variable declaration is easy to write and understand, but may lead to slower performance. The explicit `for` loop with variable assignment can be faster, but requires manual management of scope. Simple `for` loops without variables are typically fastest, but may be less readable.

Related benchmarks:

for vs for with var len (version: 2)

Compare loop performance

Comparing performance of: for a vs for b vs for c

Created: one year ago by: Registered User

Jump to the latest result

for a

for b

for c

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

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