Benchmark: for-in vs object.keys vs object.values for objects vs arr

Script Preparation code:

var obj = {
  'a': {
    id: 'a',
    num: 1
  },
  'b': {
    id: 'b',
    num: 1
  },
  'c': {
    id: 'c',
    num: 1
  },
  'd': {
    id: 'd',
    num: 1
  },
  'e': {
    id: 'e',
    num: 1
  },
  'f': {
    id: 'f',
    num: 1
  },
  'g': {
    id: 'g',
    num: 1
  },
};

var arr = [
  {
    id: 'a',
    num: 1
  },
  {
    id: 'b',
    num: 1
  },
  {
    id: 'c',
    num: 1
  },
  {
    id: 'd',
    num: 1
  },
  {
    id: 'e',
    num: 1
  },
  {
    id: 'f',
    num: 1
  },
  {
    id: 'g',
    num: 1
  }
];

Tests:

for-in
for (var i=10000; i > 0; i--) { for (var key in obj) { console.log(obj[key].id); } }
Object.keys
for (var i=10000; i > 0; i--) { Object.keys(obj).forEach(key => console.log(obj[key].id)); }
Object.values
for (var i=10000; i > 0; i--) { Object.values(obj).forEach(n => console.log(n.id)); }
Array for
for (var i=10000; i > 0; i--) { for (var j=0,l=arr.length; j < l; j++) { console.log(arr[j].id); } }
Array forEach
for (var i=10000; i > 0; i--) { arr.forEach(n => console.log(n.id)); }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
for-in
Object.keys
Object.values
Array for
Array forEach

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 tests the performance of different ways to iterate over objects and arrays in JavaScript.

**Options Compared:**

* **`for...in` (Object Iteration):**  This traditional loop iterates through the *keys* of an object. It's simple but can be slower than other methods due to its reliance on enumerating properties, which might include inherited ones.
* **`Object.keys()` (Array of Keys):** This method returns an array of the object's own keys.  It's generally faster than `for...in` because it avoids iterating through unnecessary properties.

* **`Object.values()` (Array of Values):**  Returns an array containing the *values* of an object's own properties. Useful if you need direct access to values instead of just keys.
* **`for...loop` with Array:** This standard loop iterates over each element in an array directly by index, which is usually the most efficient way to work with arrays.

* **`forEach()` (Array Iteration):** A higher-order function that executes a provided callback function for each element in an array. It offers a more concise syntax than `for...loop`.

**Pros and Cons:**

| Method | Pros                                   | Cons                             |
|--------|------------------------------------------|-----------------------------------|
| `for...in`| Simple, easy to understand           | Can be slower due to property enumeration |
| `Object.keys()`| Faster than `for...in`, returns keys as array | Doesn't return values             |
| `Object.values()` | Returns values directly         | Doesn't return keys              |
| `for...loop` (Array) | Generally the fastest for arrays  | More verbose                       |
| `forEach()`      | Concise syntax                     | Less direct control over iteration |

**Alternatives:**

While not shown in this benchmark, other methods like `map()`, `filter()`, and `reduce()` provide powerful ways to transform or analyze array data.

**Key Takeaways:**

* For arrays, using a `for...loop` or `forEach()` is generally the most efficient way to iterate. 
* `Object.keys()` and `Object.values()` are good choices when working with object keys and values respectively.  `for...in` should be used with caution due to its potential performance issues.

Let me know if you have any other questions!

Related benchmarks:

for-in vs object.keys vs object.values for objects vs arr (version: 0)

Comparing performance of: for-in vs Object.keys vs Object.values vs Array for vs Array forEach

Created: 2 years ago by: Guest

Jump to the latest result

for-in

Object.keys

Object.values

Array for

Array forEach

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):