Benchmark: Object.keys ForEach vs for-in hasOwnProperty

Script Preparation code:

// Declaring our Animal object
var Animal = function () {

    this.name = 'unknown';

    this.getName = function () {
        return this.name;
    }

    return this;
};

// Declaring our Dog object
var Dog = function () {

    // A private variable here        
    var private = 42;

    // overriding the name
    this.name = "Bello";

    // Implementing ".bark()"
    this.bark = function () {
        return 'MEOW';
    }  

    return this;
};


// Dog extends animal
Dog.prototype = new Animal();

// Creating an instance of Dog.
var obj = new Dog();

function iterateA() {
  var ret = "";
    
  for (var prop in obj) {
    if( obj.hasOwnProperty( prop ) ) {
      ret += obj[prop];
    } 
  }
    
  return ret;
}

function iterateB() {
  var ret = "";
    
  Object.keys(obj).forEach(function (prop) {
    ret += obj[prop];
  });

  return ret;
}

function iterateC() {
   var ret = "";

   for (var i = 0, keys = Object.keys(obj); i < keys.length; i++) {
       ret += obj[i];
   }

   return ret;
}

function iterateD() {
   var ret = "";

   for (var keys = Object.keys(obj), len = keys.length, i = 0; i < len; i++) {
       ret += obj[i];
   }

   return ret;
}

Tests:

A
var tmp = iterateA();
B
var tmp = iterateB();
C
var tmp = iterateC();
D
var tmp = iterateD();

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
A
B
C
D

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 2 years ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/119.0.0.0 Safari/537.36

Browser/OS: Chrome 119 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
A	2406405.2 Ops/sec
B	3221296.2 Ops/sec
C	4528368.5 Ops/sec
D	4542309.0 Ops/sec

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

LLMs can make mistakes. Check important info.

**Benchmark Explanation**

The provided benchmark measures the performance of different approaches to iterate over an object's properties in JavaScript. The test cases use two objects, `Animal` and `Dog`, which are created using the `function` keyword.

**Object.keys() vs for-in hasOwnProperty**

The benchmark compares the performance of three methods:

1. **for-in hasOwnProperty**: This method iterates over the object's own enumerable properties (using `hasOwnProperty()` to filter out inherited properties).
2. **Object.keys().forEach()**: This method uses the `Object.keys()` function to get an array of the object's property names, and then iterates over that array using `forEach()`.
3. **Manual iteration using for loops**: Two additional methods are used: `iterateC()` and `iterateD()`, which use traditional `for` loops with `Object.keys()` and indexing into the array, respectively.

**Options Comparison**

Here's a brief summary of each option:

* **For-in hasOwnProperty**: This method is generally considered the most efficient way to iterate over an object's own properties. However, it can be slower than using `Object.keys()` if the object has many inherited properties.
* **Object.keys().forEach()**: This method is convenient and easy to read, but it creates a new array of property names, which can lead to higher memory usage. Additionally, `forEach()` can be slower than traditional `for` loops due to its overhead.
* **Manual iteration using for loops**:
	+ `iterateC()`: Uses indexing into the `Object.keys()` array, which can lead to slower performance due to the need to calculate the array length and bounds.
	+ `iterateD()`: Similar to `iterateC()`, but uses a more concise syntax by calculating the array length and loop bounds directly.

**Pros and Cons**

* **For-in hasOwnProperty**: Pros: efficient, easy to read. Cons: can be slower if object has many inherited properties.
* **Object.keys().forEach()**: Pros: convenient, easy to read. Cons: creates new array of property names, potentially slower due to overhead.
* **Manual iteration using for loops**: Pros: control over loop bounds and indexing, cons: can be slower due to indexing calculations.

**Library Usage**

None of the test cases explicitly use a library or external dependency.

**Special JS Features/Syntax**

The benchmark uses JavaScript features like `function` declarations, object creation, property names, and array iteration methods. However, these are standard JavaScript features and do not require special knowledge or expertise to understand.

**Alternatives**

If you were to rewrite this benchmark, you might consider additional alternatives, such as:

* Using a different data structure, like an array or a Map.
* Introducing more complex logic or side effects within the iteration loop.
* Using async/await or callbacks for asynchronous iterations.
* Using web workers or other parallel execution techniques.

Related benchmarks:

Object.keys ForEach vs for-in hasOwnProperty (version: 0)

Original source: https://jsperf.com/object-keys-foreach-vs-for-in-hasownproperty

Comparing performance of: A vs B vs C vs D

Created: 5 years ago by: Registered User

Jump to the latest result

A

B

C

D

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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