Benchmark: [key, value] of Object.entries vs for..in

Script Preparation code:

var obj = {
	a: 1,
    b: 2,
	c: 3,
	d: 4,
	0: 'a',
  	1: 'b',
  	str: 'long string',
	nested: {
    	nested: 0
    },
	hello: 55.5
};

Tests:

[key, value] of Object.entries(obj)
for (let i = 0; i < 10000; i++) { for (const [key, value] of Object.entries(obj)) { console.log(key, value); } }
key in ob
for (let i = 0; i < 10000; i++) { for (const key in obj) { const value = obj[key]; console.log(key, value); } }
for i Object.entries
for (let i = 0; i < 10000; i++) { for (let entries = Object.entries(obj), i = entries.length - 1, entry = entries[i]; i >= 0; entry = entries[i--]) { const [key, value] = entry; console.log(key, value); } }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
[key, value] of Object.entries(obj)
key in ob
for i 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; rv:109.0) Gecko/20100101 Firefox/111.0

Browser/OS: Firefox 111 on Mac OS X 10.15

View result in a separate tab

Test name	Executions per second
[key, value] of Object.entries(obj)	3.0 Ops/sec
key in ob	2.7 Ops/sec
for i Object.entries	2.7 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark JSON and explore what's being tested, compared, and their pros and cons.

**Benchmark Definition**

The benchmark defines two approaches to iterate over an object:

1. `[key, value] of Object.entries`: This approach uses the `Object.entries` method to get an array of key-value pairs from the object, and then iterates over it using a `for...of` loop.
2. `for (const key in obj)`: This approach uses the `in` operator to iterate over the object's own enumerable properties (i.e., keys), and then accesses the corresponding value using the `obj[key]` syntax.

**Comparison**

The benchmark compares these two approaches, measuring their performance by executing each one 10,000 times. The goal is to determine which approach is faster.

**Pros and Cons of Each Approach**

1. `[key, value] of Object.entries`:
	* Pros: This approach is more concise and readable, as it uses a standard JavaScript method (`Object.entries`) and a `for...of` loop.
	* Cons: Since `Object.entries` returns an array of key-value pairs, this approach might be slower than iterating directly over the object's keys. However, modern JavaScript engines are optimized for `Object.entries`, making this approach competitive.
2. `for (const key in obj)`:
	* Pros: This approach is potentially faster since it iterates directly over the object's keys without creating an array or using a loop. However, it relies on the `in` operator, which might lead to slower performance due to the overhead of resolving property names.
	* Cons: The syntax can be less readable and more error-prone than the `[key, value] of Object.entries` approach.

**Library Used**

In this benchmark, `Object.entries` is used as a built-in JavaScript method. There's no external library involved.

**Special JS Feature or Syntax**

The benchmark uses modern JavaScript features like:

* `for...of` loops
* Template literals (`\r\n`)
* Object literal syntax (e.g., `var obj = {...}`)

These features are widely supported by modern browsers, including Firefox 111.

**Other Alternatives**

If you want to explore alternative approaches or libraries for iterating over objects in JavaScript, consider the following options:

* Using `for...in` loops instead of `for...of` loops
* Utilizing the `forEach()` method on an array created from the object's keys (e.g., `[Object.keys(obj)]`)
* Leveraging a library like Lodash or Ramda for functional programming approaches

However, keep in mind that the built-in JavaScript methods (`Object.entries`, `for...of`) and loops are often optimized for performance and should be the primary choice for most use cases.

Related benchmarks:

[key, value] of Object.entries vs for..in (version: 0)

Comparing performance of: [key, value] of Object.entries(obj) vs key in ob vs for i Object.entries

Created: one year ago by: Guest

Jump to the latest result

[key, value] of Object.entries(obj)

key in ob

for i Object.entries

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

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