Benchmark: javascript loops performance

Script Preparation code:

var arr = new Array(100000).fill(Math.random());
var lastValue = 0;

Tests:

for
for (var i = 0; i < arr.length; i++) { lastValue = arr[i]; }
for_in
for (var i in arr) { lastValue = arr[i]; }
for_of
for (var v of arr) { lastValue = v; }
forEach
arr.forEach(v => lastValue = v);
map
arr.map(v => lastValue = v);
while
let i = 0; while(i < arr.length) { lastValue = arr[i]; i++; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
for
for_in
for_of
forEach
map
while

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 benchmark and its components.

**Benchmark Purpose:**
The goal of this benchmark is to compare the performance of different loop structures in JavaScript, specifically:

* `for` loops
* `for...in` loops (which iterate over an object's properties)
* `for...of` loops (which iterate over an array or other iterable)
* `forEach`
* `map`

**Loop Structures Compared:**
The benchmark compares the performance of these five loop structures on a specific test case: iterating over an array and assigning a value to a variable (`lastValue`) in each iteration.

**Options Compared:**

1. **`for` loops**: Iterate manually using `i = 0; while(i < arr.length) { ... }`.
2. **`for...in` loops**: Iterate over the array's properties, but assign the value to `lastValue` directly.
3. **`for...of` loops**: Iterate over the array and assign the value to `lastValue` in each iteration.
4. **`forEach`**: Use the `forEach` method to iterate over the array and execute a callback function for each element.
5. **`map`**: Use the `map` method to create a new array with the same number of elements as the original array, but this time also assign the value to `lastValue` in each iteration.

**Pros and Cons:**

1. **`for` loops**:
	* Pros: Simple and well-understood.
	* Cons: Can be error-prone if not implemented correctly (e.g., forgetting to increment `i`).
2. **`for...in` loops**:
	* Pros: Convenient for iterating over objects, but can produce unexpected results when iterating over arrays.
	* Cons: May iterate over the array's prototype chain or other properties.
3. **`for...of` loops**:
	* Pros: Modern and efficient way to iterate over arrays.
	* Cons: Requires using a variable (`v`) to store each value, which can be slower than direct assignment.
4. **`forEach`**:
	* Pros: Convenient for iterating over arrays and executing a callback function.
	* Cons: May not be as efficient as other options (e.g., `for...of` loops) due to the overhead of the callback function.
5. **`map`**:
	* Pros: Useful for creating new arrays with transformed data, but can produce unexpected results if not used correctly.
	* Cons: Iterates over the original array and produces additional overhead due to the map operation.

**Library Used:**
The `forEach` and `map` methods are part of the JavaScript language itself, so no libraries are required for these options.

**Special JS Feature/Syntax:**
There is no special JS feature or syntax used in this benchmark. The focus is on comparing different loop structures and their performance characteristics.

**Alternatives:**

* **Other iteration methods**: Other iteration methods, such as `while` loops with manual indexing (`arr[i]`) or using `Array.prototype.reduce()`, could also be included in the benchmark to compare their performance.
* **Native array operations**: Native array operations like `reduce()` or `every()` could be used instead of traditional loops to create a more modern and efficient comparison.
* **Async iterations**: Asynchronous iterations, such as using `async/await` with a callback function, could be added to the benchmark to simulate real-world scenarios where performance differences are critical.

Related benchmarks:

javascript loops performance (version: 0)

test js each loops performance

Comparing performance of: for vs for_in vs for_of vs forEach vs map vs while

Created: 3 years ago by: Guest

Jump to the latest result

for

for_in

for_of

forEach

map

while

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):