Benchmark: for in vs object keys filter

Script Preparation code:

var obj = {
    a: {
        isList: true
    },
    b: {
        isList: false
    },
    c: {
        isList: true
    },
    d: {
        isList: false
    },
    e: {
        isList: true
    },
    f: {
        isList: true
    }
};

Tests:

For IN
const arr = []; for (let prop in obj) { if (obj[prop].isList) { arr.push(prop); } } console.log(arr);
Object Keys Filter
const arr = Object.keys(obj).filter(prop => obj[prop].isList); console.log(arr);

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
For IN
Object Keys Filter

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.

Let's dive into the world of JavaScript microbenchmarks.

**Benchmark Overview**

The provided benchmark compares two approaches for filtering an object's properties using `for...in` loop and `Object.keys()` method with `filter()`. The test case is designed to measure which approach is faster, more efficient, or both.

**Options Compared**

Two options are compared:

1. **For-in Loop**: This approach uses a traditional `for...in` loop to iterate over the object's properties.
2. **Object Keys Filter**: This approach uses the `Object.keys()` method to get an array of the object's property names, and then filters this array using the `filter()` method.

**Pros and Cons**

### For-in Loop

Pros:

* More intuitive for developers who are familiar with traditional loops
* May be faster for small objects or objects with a limited number of properties

Cons:

* Can be slower for large objects due to the overhead of iterating over all properties
* May not work as expected if the object has inherited properties (due to the `for...in` loop including these)

### Object Keys Filter

Pros:

* Generally faster than the traditional `for...in` loop, especially for large objects
* More concise and easier to read
* Works correctly even when dealing with inherited properties

Cons:

* May require more memory to store the array of property names
* Can be slower if the object has a large number of properties (due to the overhead of creating the array)

**Library Usage**

The test case does not explicitly use any libraries, but it relies on built-in JavaScript methods like `Object.keys()` and `filter()`. These methods are part of the ECMAScript standard and do not require any additional libraries.

**Special JS Feature or Syntax**

There is no special JavaScript feature or syntax used in this benchmark. The test case only uses standard JavaScript constructs like loops, arrays, and object iteration.

**Alternatives**

If you're looking for alternative approaches to filter an object's properties, here are a few options:

1. **Using `forEach()` method**: Instead of using `filter()`, you can use the `forEach()` method with a callback function to iterate over the property names.
2. **Using `reduce()` method**: You can use the `reduce()` method to accumulate an array of property names that meet the condition.
3. **Using `Object.entries()` and `some()` methods**: This approach uses the `Object.entries()` method to get an array of key-value pairs, and then uses the `some()` method with a callback function to filter out properties.

For example:

```javascript
const arr = Object.entries(obj).filter(([prop, value]) => value.isList);
```

Keep in mind that these alternatives may have different performance characteristics depending on the specific use case.

Related benchmarks:

for in vs object keys filter (version: 0)

battle of the object key loops

Comparing performance of: For IN vs Object Keys Filter

Created: 4 years ago by: Guest

Jump to the latest result

For IN

Object Keys Filter

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):