Benchmark: for vs foreach vs for..of vs for..of over entries vs for in

Script Preparation code:

var array = Array.from({length: 100});
var t;

Tests:

for
for (let i = 0; i < array.length; i++) { t = array[i]; }
foreach
array.forEach(function(v, i) { t = v; });
for..of
for (var v of array) { t = v; }
for..of over entries
for (var [i, v] of array.entries()) { t = v; }
for..in
for (var k in array) { t = array[k]; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
for
foreach
for..of
for..of over entries
for..in

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/136.0.0.0 Safari/537.36

Browser/OS: Chrome 136 on Windows

View result in a separate tab

Test name	Executions per second
for	78832.0 Ops/sec
foreach	79589.6 Ops/sec
for..of	78262.2 Ops/sec
for..of over entries	76072.1 Ops/sec
for..in	68624.8 Ops/sec

Autogenerated LLM Summary (model llama3.1:latest, generated one year ago):

LLMs can make mistakes. Check important info.

Let's break down what is being tested and compared here.

**What is being tested?**

The benchmark is testing the performance of different ways to iterate over an array in JavaScript: `for`, `forEach`, `for...of`, `for...of` over `entries`, and `for...in`.

**What options are compared?**

Here are the five test cases:

1. **`for`**: A traditional `for` loop with a counter variable `i`.
2. **`forEach`**: Using the `Array.prototype.forEach()` method to iterate over the array.
3. **`for...of`**: Using a `for...of` loop to iterate directly over the array values.
4. **`for...of` over entries**: Using a `for...of` loop to iterate over the key-value pairs of an array using `entries()`.
5. **`for...in`**: Using a `for...in` loop to iterate over the property names ( indices ) of an object, but here we are using it on an array.

**Pros and Cons:**

Here's a brief summary:

* **`for`**: Pros: simple, familiar syntax; Cons: requires indexing variable.
* **`forEach`**: Pros: concise syntax for iterating over arrays; Cons: may not be suitable for large datasets or performance-critical code.
* **`for...of`**: Pros: concise and expressive syntax; Cons: may not work with older browsers (e.g., IE).
* **`for...of` over entries**: Pros: allows iteration over both key-value pairs and array indices; Cons: requires modern JavaScript features (`entries()` method).
* **`for...in`**: Note that using `for...in` on an array is generally discouraged, as it iterates over the property names (indices) rather than the actual values. This can lead to unexpected behavior if the array has non-index properties.

**Library usage:**

None of these test cases use a specific library. The only external function used is `Array.from()` in the script preparation code.

**Special JS features or syntax:**

* **`for...of`**: This loop syntax was introduced in ECMAScript 2015 (ES6).
* **`entries()` method**: This method returns an array iterator that yields key-value pairs for each entry in an object. It was also introduced in ES6.
* **Array.from()**: This method creates a new, dense array from an iterable or an array-like object.

**Other alternatives:**

For iterating over arrays, you can also use:

* `map()` or `filter()` methods (if you need to transform or filter the data)
* A simple index-based loop (like `for` loops) when performance is not a concern
* Modern JavaScript features like `reduce()`, `every()`, and `some()` (when applicable)

Please note that this answer provides a general overview, and the best approach will depend on the specific use case and requirements.

Related benchmarks:

for vs foreach vs for..of vs for..of over entries vs for in (version: 0)

Compare loop performance

Comparing performance of: for vs foreach vs for..of vs for..of over entries vs for..in

Created: 2 years ago by: Guest

Jump to the latest result

for

foreach

for..of

for..of over entries

for..in

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.1:latest, generated one year ago):