Benchmark: Object iteration for-in vs object.keys

Script Preparation code:

var obj = {};
for (var i = 10000; i > 0; i--) {
    obj[`key ${i}`] = i;
}

Tests:

for-in
for (var key in obj) { console.log(obj[key]); }
Object.keys
Object.keys(obj).forEach(key => console.log(obj[key]));

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
for-in
Object.keys

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/135.0.0.0 Safari/537.36

Browser/OS: Chrome 135 on Windows

View result in a separate tab

Test name	Executions per second
for-in	40.5 Ops/sec
Object.keys	41.3 Ops/sec

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

LLMs can make mistakes. Check important info.

**Benchmark Explanation**

MeasureThat.net is testing the performance of two different approaches for iterating over an object in JavaScript: `for-in` and `Object.keys()`. The benchmark definition provides a simple object with 10,000 properties, each initialized with a unique value.

**Approaches Comparison**

1. **For-in loop**: This approach iterates over the object's properties using a traditional `for` loop with an array-like index (`key`). It prints the value of each property to the console.
2. **Object.keys() and forEach**: This approach uses the built-in `Object.keys()` method to get an array of the object's property names, which is then iterated over using the `forEach` method, printing the corresponding property values.

**Pros and Cons**

* **For-in loop**:
	+ Pros: Simple and straightforward implementation.
	+ Cons: May not be as efficient as other approaches due to the overhead of iterating over an array-like index.
* **Object.keys() and forEach**:
	+ Pros: More modern and efficient approach, leveraging built-in JavaScript methods.
	+ Cons: Requires a slightly more complex setup.

**Library and Special JS Features**

Neither benchmark definition uses any external libraries or special JavaScript features. However, it's worth noting that `Object.keys()` is a relatively modern feature introduced in ECMAScript 2015 (ES6).

**Test Case Explanation**

The individual test cases are:

1. **For-in**: Iterates over the object's properties using a traditional `for` loop with an array-like index (`key`). It prints the value of each property to the console.
2. **Object.keys() and forEach**: Uses the built-in `Object.keys()` method to get an array of the object's property names, which is then iterated over using the `forEach` method, printing the corresponding property values.

**Other Alternatives**

Alternative approaches could include:

1. Using a library like Lodash or Underscore.js for more efficient iteration and manipulation of objects.
2. Utilizing modern JavaScript features like `for...of` loops or iterators to simplify object iteration.
3. Implementing a custom iterator function using the `Symbol.iterator` method.

However, these alternatives may not be directly comparable to the `for-in` and `Object.keys()` approaches, as they would require additional setup and potentially alter the benchmark's results.

Related benchmarks:

Object iteration for-in vs object.keys (version: 0)

Comparing performance of: for-in vs Object.keys

Created: 4 years ago by: Guest

Jump to the latest result

for-in

Object.keys

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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