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:

No previous run results

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Autogenerated LLM Summary (model gemma2:9b, generated one year ago):

LLMs can make mistakes. Check important info.

This benchmark compares two ways to iterate over the properties of a JavaScript object: using `for...in` and using `Object.keys`.

**`for...in`:**

* **Description:** This traditional method iterates through each property name (key) in an object. The `hasOwnProperty()` check is included to avoid iterating over inherited properties, which might not be desired.
* **Pros:**  More concise syntax, can work with any object regardless of whether it has a defined keys array. 
* **Cons:** Slower than `Object.keys` in modern JavaScript engines because it relies on implicit iteration and property descriptor checks. Can also be more complex to understand for beginners.

**`Object.keys`:**

* **Description:** This method returns an array containing all the enumerable property names of an object. You then iterate over this array using a `for` loop.
* **Pros:**  Generally faster than `for...in` because it avoids unnecessary checks and provides a predictable iteration order. 
* **Cons:** Requires an extra step to call `Object.keys()` and iterate over the returned array, which can be slightly less concise.

**Benchmark Results:**

The benchmark results show that `Object.keys` is consistently faster than `for...in` in this specific case.  This aligns with general performance expectations.

**Alternatives:**

* **Modern JavaScript Iterators:** For more advanced scenarios and potentially better performance, you could consider using modern iterators and the `for...of` loop to iterate over the object's values.

```javascript
   const obj = { a: 1, b: 2 };

for (const value of Object.values(obj)) {
       console.log(value);
   }
   ```

* **Libraries:** While this benchmark doesn't use libraries, there are specific JavaScript libraries designed for optimizing object manipulation and iteration if your use case demands it.

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 gemma2:9b, generated one year ago):