Benchmark: for-in vs object.keys + for

Script Preparation code:

var obj = {
  'a': 1,
  'b': 1,
  'c': 1,
  'd': 1,
  'e': 1,
  'f': 1,
  'g': 1
};

Tests:

for-in
const result = []; for (var key in obj) { result.push(key, obj[key]); }
Object.keys
const result = []; const keys = Object.keys(obj); for (let i = 0; i < keys.length; i++) { const key = keys[i]; result.push(key, obj[key]); }

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 llama3.2:3b, generated one year ago):

LLMs can make mistakes. Check important info.

Measuring different approaches to iterating over objects in JavaScript can be an interesting benchmark.

**What is being tested?**

The provided JSON represents two individual test cases:

1.  **`for-in` loop**: This test case measures the performance of using the `for...in` loop to iterate over the properties of an object.
2.  **`Object.keys()` + `for` loop**: This test case measures the performance of using the `Object.keys()` method to get an array of an object's property names, followed by a traditional `for` loop to iterate over those names.

**Options compared**

The two approaches being tested are:

1.  **Traditional `for-in` loop**: Iterates directly over the properties of an object without requiring any additional setup.
2.  **Using `Object.keys()` + traditional `for` loop**: Requires more setup, but can provide better performance due to optimized internal implementation.

**Pros and Cons**

*   **For-in Loop**
    *   Pros:
        *   Simple to implement
        *   Portable across different browsers
    *   Cons:
        *   Can be slower due to the need to check for undefined values in each iteration.
        *   May not work correctly if the object's prototype is modified.
*   **Object.keys() + For Loop**
    *   Pros:
        *   Often faster than traditional `for-in` loop due to optimized internal implementation
        *   More robust and reliable, as it doesn't have issues with undefined values or prototype modifications
    *   Cons:
        *   Requires more setup (getting the array of property names)
        *   May require additional polyfills for older browsers

**Library Usage**

In this benchmark, the `Object.keys()` method is used. This method is a part of the ECMAScript Standard and is supported by most modern browsers.

However, if you're targeting an older browser that doesn't support `Object.keys()`, you might need to use a polyfill or alternative approach (e.g., using `for...in` loop with `Object.getOwnPropertyNames()` or `forEach()`).

**Special JS Features/Syntax**

There are no special JavaScript features or syntax used in this benchmark. The tests only utilize standard ECMAScript features.

**Other Alternatives**

If you need to iterate over objects and want to consider other approaches, here are a few alternatives:

1.  **Using `Array.prototype.forEach()`**: This method iterates over an array of values without requiring any additional setup.
2.  **Using `forEach` method on the object's prototype chain**: If the object has a prototype with enumerable properties, you can use `for...in` loop or `Object.keys()` to iterate over those properties.

Keep in mind that each approach has its pros and cons, and choosing the best one depends on your specific use case and performance requirements.

Related benchmarks:

for-in vs object.keys + for (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 llama3.2:3b, generated one year ago):