Benchmark: for...in vs Object.keys

Script Preparation code:

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

Tests:

for...in
for (let i = 0; i < 100000; i++) { let temp = 0; for (const key in map) { temp += map[key]; } }
Object.keys
for (let i = 0; i < 100000; i++) { let temp = 0; const keys = Object.keys(map); for (let j = 0; j < keys.length; j++) { temp += map[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 llama3.2:3b, generated one year ago):

LLMs can make mistakes. Check important info.

**What is being tested?**

On the provided JSON, two individual test cases are being measured: `for...in` and `Object.keys`. These two approaches are used to iterate over an object's keys (i.e., its properties) in JavaScript.

**Options compared**

The two options being compared are:

1. **For...in loop**: This is a traditional way of iterating over the keys of an object using a loop.
2. **`Object.keys()` method**: This is a built-in method that returns an array-like object containing the keys of an object.

**Pros and Cons**

**For...in loop:**

Pros:

* Can be used with any type of object, not just those with enumerable properties (e.g., objects with non-enumerable properties like `Symbol` properties).
* May perform better for small to medium-sized datasets.

Cons:

* Does not guarantee the order of iteration; the order may vary between browsers or JavaScript engines.
* Can be slower than using `Object.keys()` due to its dynamic nature and potential use of internal iteration mechanisms.

**`Object.keys()` method:**

Pros:

* Guaranteed order of iteration (i.e., keys are always in the same order across different browsers).
* Generally faster than using a for...in loop, especially for large datasets.

Cons:

* Only works with objects that have enumerable properties. Non-enumerable properties (e.g., `Symbol` properties) will not be included.
* May require additional processing to convert the resulting array-like object to an actual array.

**Library/Utility**

None are explicitly mentioned in this benchmark, but it's worth noting that some modern JavaScript engines and browsers may use their own internal iteration mechanisms or optimizations for iterating over objects' keys.

**Special JS feature/Syntax**

This benchmark does not require any special JavaScript features or syntax. Both test cases use standard JavaScript language constructs (i.e., `for...in` loop and the `Object.keys()` method).

**Other alternatives**

If you're interested in exploring alternative approaches, here are a few:

1. **Using `Array.from()`**: This method creates an array from an iterable object, such as an object's keys using `Object.entries()`. You can then use `forEach()` or `reduce()` to process the array.
2. **Using `for...of` loop**: This is another way of iterating over objects' properties using a loop.
3. **Manual iteration using `in` operator and indexing**: You can manually iterate over an object's keys using the `in` operator and indexing (i.e., accessing elements by their index).

Keep in mind that these alternatives may have different trade-offs, performance characteristics, or requirements for use cases.

I hope this explanation helps!

Related benchmarks:

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