Benchmark: forEach vs reduce vs for - fill object with object

Script Preparation code:

var arr = [];
for (var i = 0; i < 50000; i++) {
  arr.push(i);
}

Tests:

forEach
var objForEach = {}; arr.forEach(item => { objForEach[item] = { exists: true }; });
reduce
var objReduce = arr.reduce((acc, item) => { acc[item] = { exists: true }; return acc; }, {});
for
var objFor = {}; for (var j = 0; j < arr.length; j++) { var item = arr[j]; objFor[item] = { exists: true }; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
forEach
reduce
for

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/81.0.4044.122 Safari/537.36

Browser/OS: Chrome 81 on Windows 7

View result in a separate tab

Test name	Executions per second
forEach	86.2 Ops/sec
reduce	106.1 Ops/sec
for	17.0 Ops/sec

Autogenerated LLM Summary (model gemma2:9b, generated 6 months ago):

LLMs can make mistakes. Check important info.

This benchmark compares three different approaches to filling an object with values based on an array:

**1. `forEach`:**  Iterates through each element of the array using the `forEach` method and for each element, it adds a property to the `objForEach` object with a value indicating its existence (`{ exists: true }`).

**2. `reduce`:** Uses the `reduce` method to iterate through the array and accumulate the result in an object. For each element, it sets a property on the accumulating object representing the existence of that element.

**3. `for` Loop:**  Employs a traditional `for` loop to iterate over the array indices and uses the loop variable `j` to access elements from `arr`. It then adds properties to `objFor` based on each array element's value.

**Pros & Cons:**

* **`forEach`:**
    * **Pros:** Concise syntax, readable for beginners.  
    * **Cons:** Can be less efficient than other methods when working with large arrays and performing complex operations on each element.

* **`reduce`:** 
    * **Pros:** Often very efficient for tasks that involve accumulating a result from an array (like summing values or creating a new object). Provides a more functional programming style.
    * **Cons:**  Can be less intuitive for beginners compared to `forEach`.

* **`for` Loop:**
    * **Pros:** Fine-grained control over iteration, can be optimized for specific scenarios. 
    * **Cons:** Can be verbose and harder to read than higher-order methods like `forEach` and `reduce`.

**Other Considerations:**

* In this particular benchmark, the focus is on performance when creating an object where the keys are the array elements and the values indicate existence.
* The choice between these methods often depends on the specific task and the size of the array being processed. 
*  If you're primarily concerned with readability and simplicity, `forEach` might be a good choice.

**Alternatives:**

* **Object Literal Notation:**  Could be used to create the object directly in a single line, but it might not be as flexible for more complex scenarios: `const obj = { 0: true, 1: true, ... 49999: true };`.

Let me know if you have any other questions or would like more details about a specific aspect!

Related benchmarks:

forEach vs reduce vs for - fill object with object (version: 0)

Comparing performance of: forEach vs reduce vs for

Created: 5 years ago by: Guest

Jump to the latest result

forEach

reduce

for

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model gemma2:9b, generated 6 months ago):