Benchmark: Cached Object.keys() vs inline Object.keys()

Script Preparation code:

window.obj = {
  "a": 1,
  "b": 2,
  "c": 3,
  "d": 4,
  "e": 5,
  "f": 6,
  "g": 7,
  "h": 8,
  "i": 9,
  "j": 10,
  "k": 11,
  "l": 12,
  "m": 13,
  "n": 14,
  "o": 15,
  "p": 16,
  "q": 17,
  "r": 18,
  "s": 19,
  "t": 20,
  "u": 21,
  "v": 22,
  "w": 23,
  "x": 24,
  "y": 25,
  "z": 26,
}

window.cached = Object.keys(obj);

Tests:

Cached
window.cached.forEach((k) => console.log(k));
Uncached
Object.keys(window.obj).forEach((k) => console.log(k));

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Cached
Uncached

Fastest: N/A

Slowest: N/A

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Autogenerated LLM Summary (model llama3.2:3b, generated one year ago):

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Let's dive into the world of JavaScript microbenchmarks.

**Benchmark Definition**

The provided JSON represents a benchmark that tests two approaches to retrieving an array of object keys: `Object.keys()` with caching and inline `Object.keys()` without caching.

**Cached Object.keys() vs inline Object.keys()**

Here are the options being compared:

*   **Cached Object.keys():** This approach caches the result of `Object.keys(obj)` in a variable named `window.cached`. The benchmark then measures the time it takes to iterate over the cached array using `forEach`.
*   **Inline Object.keys():** This approach does not cache the result and instead calls `Object.keys(window.obj)` directly inside the benchmark.

Now, let's discuss the pros and cons of each approach:

### Cached Object.keys()

Pros:

*   **Faster iteration:** Since the result is cached, the first execution will be faster because it avoids the overhead of computing the array.
*   **Less memory allocation:** The cached array is already allocated in memory, so subsequent executions don't need to allocate new memory for the array.

Cons:

*   **Overhead of caching:** There's an initial cost to cache the result, which can be significant if the array is large.
*   **Limited applicability:** This approach only works well when the array doesn't change frequently.

### Inline Object.keys()

Pros:

*   **No extra memory allocation:** The array is created dynamically for each execution, avoiding any potential memory leaks.
*   **More flexible:** This approach can be more suitable if the array changes frequently or needs to be recalculated on every call.

Cons:

*   **Slower iteration:** Since the result needs to be computed every time, the execution will be slower due to the additional overhead of calculating the array.

**Library: Object.keys()**

The `Object.keys()` method is a built-in JavaScript function that returns an array of strings representing the enumerable properties found directly in an object. Its purpose is to provide a convenient way to iterate over an object's keys without having to manually loop through its properties.

**Special JS Feature/Syntax**

There isn't any specific special feature or syntax being used here, but it's essential to note that `window.cached` is a variable created outside the benchmark function. This allows the caching to work correctly by only computing the array once when the variable is first set.

Now, let's consider some alternative approaches:

*   **Using a for...in loop:** Instead of using `Object.keys()`, you could use a traditional for...in loop to iterate over the object's properties.
*   **Using a library like Lodash:** If you're working with large datasets or need more complex iteration logic, you might consider using a library like Lodash, which provides optimized functions for tasks like array iteration.

Keep in mind that these alternatives will have different performance characteristics and trade-offs compared to the cached vs. inline approach.

Related benchmarks:

Cached Object.keys() vs inline Object.keys() (version: 0)

This is to test any such browser optimisations on Object.keys(), which returns an array. How long does that array creation take?

Comparing performance of: Cached vs Uncached

Created: 4 years ago by: Guest

Jump to the latest result

Cached

Uncached

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):