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) { if (obj.hasOwnProperty(key)) { console.log(key); } } }
object keys
var keys = Object.keys(obj); for (var i=100; i > 0; i--) { for (var 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
object keys

Fastest: N/A

Slowest: N/A

Latest run results:

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Autogenerated LLM Summary (model llama3.1:latest, generated one year ago):

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Let's break down what's being tested here.

**Benchmark Description**
The benchmark is comparing the performance of two different ways to iterate over an object's properties: `for..in` and using `Object.keys()`.

**Test Case 1: for..in**
This test case uses a `for..in` loop to iterate over the properties of the `obj` object. The loop iterates from 100 down to 0, and inside the loop, it checks if each property belongs to the object using `hasOwnProperty()`. If it does, it logs the property name to the console.

**Test Case 2: Object.keys()**
This test case uses the `Object.keys()` method to get an array of the object's properties. Then, it iterates over this array using a traditional `for` loop, logging each property name to the console.

**Library Used**
No external libraries are used in these test cases.

**JavaScript Feature/Syntax Used**
No special JavaScript features or syntax are being tested here.

**Options Compared**
The two options being compared are:

1. Using a `for..in` loop to iterate over an object's properties.
2. Using `Object.keys()` to get an array of the object's properties, and then iterating over this array using a traditional `for` loop.

**Pros/Cons**

* **For..in**: Pros: concise syntax, easy to use. Cons: can be slow for large objects or arrays because it iterates over inherited properties as well.
* **Object.keys()**: Pros: fast and efficient, only returns own property names. Cons: requires an additional method call.

**Other Considerations**
In modern JavaScript, `for..in` is generally discouraged in favor of using `Object.keys()` or other methods that provide more control over iteration. However, for small objects or simple use cases, `for..in` can still be a convenient choice.

**Alternatives**
If you need to iterate over an object's properties and don't care about performance, you could also use:

* `Object.entries()`: Returns an array of key-value pairs for the object.
* A traditional `for` loop with a manual check for each property: While this approach is not shown in these test cases, it can be more efficient than `for..in` but less convenient.

In summary, this benchmark compares the performance of two common ways to iterate over an object's properties in JavaScript: using `for..in` and using `Object.keys()`. The results show that `Object.keys()` is slightly faster than `for..in` in this particular test case.

Related benchmarks:

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

Comparing performance of: for in vs object keys

Created: 5 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

No previous run results

Autogenerated LLM Summary (model llama3.1:latest, generated one year ago):