Benchmark: For in vs Object.entries

Script Preparation code:

var obj = {}
for(i=0; i<10000; i++){
  obj['key_'+i] = Math.random();
}

Tests:

For in
for(let key in obj){ console.log(`${key}: ${obj[key]}`); }
Object.entries
for (const [key, value] of Object.entries(obj)) { console.log(`${key}: ${value}`); }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
For in
Object.entries

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: one year ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/130.0.0.0 YaBrowser/24.12.0.0 Safari/537.36

Browser/OS: Yandex Browser 24 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
For in	38.1 Ops/sec
Object.entries	34.6 Ops/sec

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

LLMs can make mistakes. Check important info.

I'll break down the benchmark and explain what's being tested, compared options, pros and cons, library usage, special JavaScript features, and alternative approaches.

**Benchmark Overview**

The provided benchmark measures the performance of two loops that iterate over an object: `for...in` and `Object.entries()`. The benchmark creates a large object with 10,000 properties (key-value pairs) using a script preparation code. Then, it defines two test cases:

1. `For in`: Iterates over the object's properties using the `for...in` loop.
2. `Object.entries()`: Iterates over the object's key-value pairs using the `Object.entries()` method.

**Comparison of Loop Approaches**

The benchmark compares the performance of these two loops under different scenarios:

* **Loop iterations**: Both loops iterate 10,000 times, which simulates a large dataset.
* **Access pattern**: The `For in` loop accesses each property directly (e.g., `obj[key]`) using bracket notation. In contrast, the `Object.entries()` loop iterates over an array of key-value pairs, where each iteration accesses both the key and value.

**Pros and Cons**

**For...in Loop:**

Pros:

* Simple and intuitive syntax.
* Can be used when you need to iterate over object properties in a specific order (e.g., iterating over keys, then values).

Cons:

* Performance is slower due to the overhead of parsing the `for...in` loop and iterating over each property manually.
* May have performance issues if the object is large or has many properties.

**Object.entries() Loop:**

Pros:

* Faster performance since it leverages optimized array iteration and reduces manual property access overhead.
* Can handle large datasets efficiently, as it iterates over an array of key-value pairs.

Cons:

* Requires a modern JavaScript engine that supports `Object.entries()` (introduced in ECMAScript 2015).
* May require additional memory allocation for the temporary array created by `Object.entries()`.
* Syntax can be less familiar to developers without experience with object iteration methods.

**Library Usage**

There is no library explicitly mentioned in this benchmark. However, it's worth noting that `Object.entries()` is a built-in method in modern JavaScript engines (since ECMAScript 2015). If you needed to support older browsers or environments, you might use libraries like Lodash (`_.entries()`) or the `forEach` method.

**Special JavaScript Features**

* **For...in Loop**: This loop uses a non-standard syntax and may have performance issues due to manual property access. While it's not considered "special," its syntax can be unfamiliar to developers without experience with object iteration methods.
* **Object.entries() Method**: This method is a built-in feature introduced in ECMAScript 2015, which requires support for modern JavaScript engines.

**Alternative Approaches**

If you wanted to test other loop approaches or variations, some alternatives could include:

1. Using a `for` loop with bracket notation (`obj[key]`) instead of `For...in`.
2. Using an array-based approach with indexing (e.g., `let i = 0; while (i < obj.length) { ... }`).
3. Utilizing modern JavaScript features like `Array.prototype.map()` or `Array.prototype.forEach()`, which can simplify object iteration.

Feel free to ask if you'd like me to elaborate on any of these points!

Related benchmarks:

For in vs Object.entries (version: 0)

Comparing performance of: For in vs Object.entries

Created: 2 years ago by: Guest

Jump to the latest result

For in

Object.entries

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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