Benchmark: Array loops: for vs for in vs for of vs forEach vs map [fixed for IE]

Script Preparation code:

var arr = [];
for (let i = 0; i < 1000; i++) {
  arr[i] = i;
}

function foo(bar) {
  return bar;
}

Tests:

for
for (let i = 0, len = arr.length; i < len; i++) { foo(arr[i]); }
for in
for (let i in arr) { foo(arr[i]); }
for of
for (let val of arr) { foo(val); }
forEach
arr.forEach(function(val) { foo(val); });
map
arr.map(function(val) { return foo(val); });

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
for
for in
for of
forEach
map

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 4 months ago)

User agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/85.0.4183.127 Safari/537.36 OPR/60.3.3004.55692

Browser/OS: Opera 60 on Linux

View result in a separate tab

Test name	Executions per second
for	19258.7 Ops/sec
for in	2645.2 Ops/sec
for of	31794.7 Ops/sec
forEach	5907.8 Ops/sec
map	4446.4 Ops/sec

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 and explain what is being tested, compared, and their pros and cons.

**Benchmark Definition**

The benchmark measures the performance of different JavaScript loops for iterating over an array:

1. `for` loop
2. `for in` loop (which is deprecated)
3. `for of` loop (introduced in ECMAScript 2015)
4. `forEach` method
5. `map` method

**Options Compared**

The five options are compared to determine which one is the fastest for iterating over an array.

Here's a brief overview of each option:

* **`for` loop**: This is the traditional way of looping over an array in JavaScript. It uses a manual index variable (`i`) and checks the bounds of the array.
	+ Pros: Easy to understand, widely supported.
	+ Cons: Can be slower than other options due to the manual indexing.
* `for in` loop: This option is deprecated and should not be used for iterating over arrays. It iterates over the properties (keys) of the object, not its values.
	+ Pros: None.
	+ Cons: Slower, less reliable, and considered bad practice.
* `for of` loop: Introduced in ECMAScript 2015, this loop is designed specifically for iterating over iterable objects like arrays.
	+ Pros: Faster, more efficient, and modern.
	+ Cons: Requires ECMAScript 2015 support.
* `forEach` method: This is a built-in method on arrays that allows you to execute a callback function for each element in the array.
	+ Pros: Easy to use, widely supported.
	+ Cons: Can be slower than other options due to the overhead of the method call.
* `map` method: Another built-in method on arrays, `map` returns a new array with the results of applying a provided function to each element in the original array.
	+ Pros: Convenient for transforming data, widely supported.
	+ Cons: Can be slower than other options due to the overhead of the method call.

**Library and Special JS Features**

None of the test cases use any external libraries or special JavaScript features. They only rely on built-in JavaScript functionality.

**Other Alternatives**

If you're looking for alternative ways to iterate over arrays, some options include:

* Using `reduce()` method
* Using `every()` and `some()` methods
* Implementing a custom loop using recursion or a generator function

Keep in mind that the performance of these alternatives may vary depending on the specific use case and JavaScript engine.

**Benchmark Preparation Code**

The provided benchmark preparation code sets up an array with 1000 elements, each initialized to its index value. It also defines a simple `foo` function that takes a single argument and returns it.

**Individual Test Cases**

Each test case has a unique benchmark definition that represents the specific loop being tested. The `Test Name` field provides a clear indication of which loop is being measured.

Related benchmarks:

Array loops: for vs for in vs for of vs forEach vs map [fixed for IE] (version: 10)

Comparing performance of: for vs for in vs for of vs forEach vs map

Created: 7 years ago by: Registered User

Jump to the latest result

for

for in

for of

forEach

map

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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