Benchmark: for..of against Object.entries vs for..in

Script Preparation code:

var array = Array.from({ length: 10000 }, () => {
  const n = Math.floor(Math.random() * 100)
  if (n > 26) {
    return n
  } else {
    return String.fromCharCode('a'.charCodeAt(0) + n);
  }
});
var obj = {};
for (let i = 0; i < array.length; i++) {
  obj[i] = array[i];
}

Tests:

for..of Object.entries()
for (const [key, val] of Object.entries(obj)) { const foo = val + 'a'; }
for..in
for (const key in obj) { const val = obj[key]; const foo = val + 'a'; }
for..of Object.entries() no destructuring
for (const entry of Object.entries(obj)) { const key = entry[0]; const val = entry[1]; const foo = val + 'a'; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
for..of Object.entries()
for..in
for..of Object.entries() no destructuring

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:80.0) Gecko/20100101 Firefox/80.0

Browser/OS: Firefox 80 on Mac OS X 10.14

View result in a separate tab

Test name	Executions per second
for..of Object.entries()	466.6 Ops/sec
for..in	740.8 Ops/sec
for..of Object.entries() no destructuring	556.4 Ops/sec

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

LLMs can make mistakes. Check important info.

**Benchmark Explanation**

The provided JSON represents a JavaScript microbenchmark test case, specifically comparing the performance of three different approaches:

1. `for...in` loop
2. Using `Object.entries()` and destructuring in a `for...of` loop
3. Using `Object.entries()` without destructuring in a `for...of` loop

The benchmark is designed to measure the execution speed of these three approaches on a large array of objects, created using `Array.from()`. The array contains 10,000 elements, each with a random value between 0 and 100. For values greater than 26, a character string is generated using `String.fromCharCode()`.

**Options Comparison**

Here's a brief overview of the options being compared:

* **`for...in` loop**: This approach iterates over the object's properties using the property name as the iteration variable. It's an older method that was commonly used before the introduction of `Object.entries()`.
	+ Pros: Simple, widely supported.
	+ Cons: May not be the fastest or most efficient way to iterate over an object's properties.
* **`Object.entries()` and destructuring in a `for...of` loop**: This approach uses the `Object.entries()` method to get an array of key-value pairs from the object, which is then iterated over using a `for...of` loop with destructuring.
	+ Pros: More efficient than `for...in`, as it avoids the overhead of property name lookups. Destructuring can also simplify the iteration logic.
	+ Cons: May not be supported in older browsers or environments that don't have access to modern JavaScript features.
* **`Object.entries()` without destructuring in a `for...of` loop**: This approach is similar to the previous one, but instead of using destructuring, it assigns the key and value variables directly from the iteration variable.
	+ Pros: Similar efficiency benefits as before, with added flexibility for custom iteration logic.
	+ Cons: Requires an extra assignment statement, which might incur a slight performance penalty.

**Library Considerations**

The benchmark uses `Object.entries()` to get an array of key-value pairs from the object. This method is part of the ECMAScript standard since ES6 (2015), so it's widely supported in modern browsers and environments.

**Special JS Feature/Syntax**

There are no special JavaScript features or syntax used in this benchmark, other than the use of `String.fromCharCode()` for generating character strings, which is a built-in method. The benchmark focuses on comparing the performance of different iteration approaches, rather than leveraging advanced JavaScript features.

**Alternative Approaches**

Other alternatives to these three approaches might include:

* Using `for...of` loop with an index variable instead of destructuring
* Using `forEach()` or other array methods for iterating over the object's properties
* Using a custom iterator function or a library like Lodash for iteration

Keep in mind that these alternative approaches might not be as efficient or scalable as the original three options, especially for large datasets.

Related benchmarks:

for..of against Object.entries vs for..in (version: 0)

Comparing performance of: for..of Object.entries() vs for..in vs for..of Object.entries() no destructuring

Created: 4 years ago by: Guest

Jump to the latest result

for..of Object.entries()

for..in

for..of Object.entries() no destructuring

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

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