Benchmark: for..in vs for loop with Object.keys

Script Preparation code:

var obj = {
  'a': 1,
  'b': 1,
  'c': 1,
  'd': 1,
  'e': 1,
  'f': 1,
  'g': 1,
  'h': 1,
  'i': 1,
  'j': 1,
  'k': 1,
  'l': 1,
  'm': 1,
  'n': 1,
  'o': 1,
  'p': 1,
  'q': 1,
  'r': 1,
  's': 1,
  't': 1,
  'u': 1,
  'v': 1,
  'w': 1,
  'x': 1,
  'y': 1,
  'z': 1,
  'aa': 1,
  'ba': 1,
  'ca': 1,
  'da': 1,
  'ea': 1,
  'fa': 1,
  'ga': 1,
  'ha': 1,
  'ia': 1,
  'ja': 1,
  'ka': 1,
  'la': 1,
  'ma': 1,
  'na': 1,
  'oa': 1,
  'pa': 1,
  'qa': 1,
  'ra': 1,
  'sa': 1,
  'ta': 1,
  'ua': 1,
  'va': 1,
  'wa': 1,
  'xa': 1,
  'ya': 1,
  'za': 1,
  'ab': 1,
  'bb': 1,
  'cb': 1,
  'db': 1,
  'eb': 1,
  'fb': 1,
  'gb': 1,
  'hb': 1,
  'ib': 1,
  'jb': 1,
  'kb': 1,
  'lb': 1,
  'mb': 1,
  'nb': 1,
  'ob': 1,
  'pb': 1,
  'qb': 1,
  'rb': 1,
  'sb': 1,
  'tb': 1,
  'ub': 1,
  'vb': 1,
  'wb': 1,
  'xb': 1,
  'yb': 1,
  'zb': 1
};

Tests:

for-in
for (let i=100; i > 0; i--) { for (const key in obj) { console.log(key); } }
for keys
var keys = Object.keys(obj); for (let i=100; i > 0; i--) { for (let j = 0; j < keys.length; j ++) { console.log(keys[j]); } }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
for-in
for keys

Fastest: N/A

Slowest: N/A

Latest run results:

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

LLMs can make mistakes. Check important info.

Let's dive into the benchmark and explain what's being tested.

**Benchmark Definition**

The benchmark measures the performance difference between two approaches: `for...in` loop and using `Object.keys()` to iterate over an object.

**Options Compared**

1. **For...in Loop**: This approach uses a traditional `for` loop with an `in` keyword to iterate over the properties of an object. The loop variable (`key`) takes on each property name in sequence, allowing for direct access to the property values.
2. **For Keys Loop with Object.keys()**: This approach uses `Object.keys()` to get an array of property names from the object, and then iterates over this array using a traditional `for` loop.

**Pros and Cons**

1. **For...in Loop**:
	* Pros: Can directly access property values without indexing, often more readable for simple cases.
	* Cons: May iterate over inherited properties (not explicitly listed in the object), can be slower due to potential array creation on older browsers.
2. **For Keys Loop with Object.keys()**:
	* Pros: Avoids iterating over inherited properties, generally faster due to avoidance of potential array creation on older browsers.
	* Cons: Requires explicit use of `Object.keys()` and array iteration, may lead to less readable code.

**Library Used**

In this benchmark, `Object.keys()` is used from the JavaScript Standard Library. Its purpose is to return an array-like object containing all property names (keys) available in the specified object.

**Special JS Feature/Syntax**

This benchmark does not use any special features or syntax like async/await, generators, or ES6 modules.

**Alternatives**

Other alternatives for iterating over objects in JavaScript include:

1. **Using `for...of` loop**: This approach uses a traditional `for` loop with an `of` keyword to iterate directly over property names (similar to the "For Keys Loop" option).
2. **Using `Array.prototype.forEach()` or `Array.prototype.forEach.call()`**: These approaches use array methods to iterate over property names, which can be more readable but may not always provide direct access to property values.

In summary, this benchmark measures the performance difference between two common ways of iterating over objects in JavaScript: using a traditional `for...in` loop versus using `Object.keys()` and explicit array iteration.

Related benchmarks:

for..in vs for loop with Object.keys (version: 0)

Comparing performance of: for-in vs for keys

Created: 5 years ago by: Guest

Jump to the latest result

for-in

for keys

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

No previous run results

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