Benchmark: for in: cache vs no-cache

Script Preparation code:

const obj = window.obj = {
  data: new Array(2e5).fill().map((v, k) => ({ ['k' + k]: k}))
}

const callback = window.callback = (value, key) => {}

Tests:

Cache
const data = obj.data; for (const key in data) { if (data.hasOwnProperty(key)) { callback(data[key], key); } }
No Cache
for (const key in obj.data) { if (obj.data.hasOwnProperty(key)) { callback(obj.data[key], key); } }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Cache
No Cache

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: one year ago)

User agent: Mozilla/5.0 (Linux; Android 10; K) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/124.0.0.0 Mobile Safari/537.36

Browser/OS: Chrome Mobile 124 on Android

View result in a separate tab

Test name	Executions per second
Cache	6.1 Ops/sec
No Cache	3.6 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark and explain what is being tested.

**Benchmark Overview**

The provided JSON represents a JavaScript microbenchmark that compares two approaches to iterating over an object: using `for...in` with caching (`Cache`) versus without caching (`No Cache`). The test measures the execution speed of these two approaches on different browsers and devices.

**Options Compared**

Two options are being compared:

1. **Cache**: This approach uses caching to store the result of `data[key]` in a variable before executing the callback function. The idea is that this will reduce the number of times the property lookup occurs, resulting in faster execution.
2. **No Cache**: This approach does not use any caching and relies solely on the `hasOwnProperty()` method to determine whether the property exists.

**Pros and Cons**

**Cache Approach:**

Pros:

* Potential performance improvement due to reduced property lookups
* Simplifies the code by avoiding the need for explicit checks

Cons:

* Requires an additional variable to store the cached result, which may increase memory usage
* May not be beneficial if the object is small or has a simple structure

**No Cache Approach:**

Pros:

* Does not require any additional variables, keeping memory usage low
* Can be beneficial for objects with complex structures or large datasets

Cons:

* May incur more performance overhead due to repeated property lookups
* Requires explicit checks using `hasOwnProperty()` to avoid errors

**Library Usage**

The test uses the `callback` function provided by the benchmarking framework, which takes two arguments: `value` and `key`. The purpose of this library is not explicitly stated, but it likely provides a way to execute code in a controlled environment while measuring performance.

**Special JS Feature or Syntax**

There are no special JavaScript features or syntax mentioned in the provided code. However, it's worth noting that some modern browsers may optimize certain properties (e.g., `length` and `property descriptors`) for faster access.

**Other Alternatives**

If you're interested in exploring alternative approaches to iterating over objects, here are a few options:

* **For...of**: This is a more modern approach that avoids the need for explicit checks using `hasOwnProperty()`. However, it may not be supported in older browsers.
* **Array.prototype.forEach()**: This method provides an efficient way to iterate over arrays without caching results. However, it requires the array to be converted into an object first (using `Object.assign()` or a similar approach).
* **Object.keys() and Array.from()**: These methods provide an efficient way to get an array of object property keys while avoiding explicit checks for existence.

These alternatives may have different performance characteristics and are best suited for specific use cases.

Related benchmarks:

for in: cache vs no-cache (version: 0)

Comparing performance of: Cache vs No Cache

Created: 3 years ago by: Guest

Jump to the latest result

Cache

No Cache

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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