Benchmark: for in vs object.keys

Script Preparation code:

var obj = {};

for (let i = 0; i <= 1000000; i++) {
  obj[`prop_${i}`] = i;
}

Tests:

for in
for (const key in obj) { let x = obj[key]; }
object.keys
const keys = Object.keys(obj); for (const key of keys) { let x = 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:

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.

I'd be happy to help you understand the JavaScript microbenchmark on MeasureThat.net.

**Benchmark Definition**

The benchmark definition represents the test case that will be executed. In this case, there are two test cases: "for in" and "object.keys". Both test cases aim to measure the performance of accessing properties of an object using different approaches.

**Script Preparation Code**

The script preparation code is a JavaScript snippet that creates an empty object `obj` with 1 million properties. The purpose of this code is to provide a large dataset for testing.

```javascript
var obj = {};
for (let i = 0; i <= 1000000; i++) {
  obj[`prop_${i}`] = i;
}
```

This code creates an object with 1 million properties, where each property has a unique key. This will be used to test the performance of accessing properties using different approaches.

**Html Preparation Code**

The html preparation code is empty in this case, which means that no HTML-related setup is required for the benchmark.

**Test Cases**

There are two test cases:

1. **"for in"`**: This test case uses a traditional `for` loop with `in` operator to access properties of the object.
```javascript
for (const key in obj) {
  let x = obj[key];
}
```

This approach is simple and widely supported, but it has some limitations. For example, it can be slower for large objects due to the overhead of iterating over all property names.

2. **"object.keys"`**: This test case uses the `Object.keys()` method to get an array of property names, which are then iterated using a `for...of` loop.
```javascript
const keys = Object.keys(obj);
for (const key of keys) {
  let x = obj[key];
}
```

This approach is more efficient than the traditional `for in` loop because it avoids iterating over all property names and instead directly iterates over the property values.

**Library**

There is no explicit library mentioned in this benchmark. However, the `Object.keys()` method is a built-in JavaScript method that returns an array of property names for an object.

**Special JS Feature or Syntax**

There are no special JavaScript features or syntaxes used in these test cases.

**Pros and Cons of Different Approaches**

* **Traditional "for in"`:
	+ Pros: Simple and widely supported.
	+ Cons: Can be slower for large objects due to the overhead of iterating over all property names.
* **"object.keys"`:
	+ Pros: More efficient than traditional `for in` loop.
	+ Cons: Requires the use of `Object.keys()` method, which may not be supported in older browsers.

**Other Alternatives**

If you want to explore alternative approaches for accessing properties of an object, here are a few options:

* **Using array indices**: You can access properties using array indices instead of property names. For example:
```javascript
for (let i = 0; i < obj.length; i++) {
  let x = obj[i];
}
```
This approach is more efficient than traditional `for in` loop but may not be as readable.

* **Using a custom iterator**: You can create a custom iterator to access properties of an object. For example:
```javascript
function* iterate(obj) {
  for (const key in obj) {
    yield obj[key];
  }
}

for (const value of iterate(obj)) {
  console.log(value);
}
```
This approach provides more control over the iteration process but may require more code.

Overall, the choice of approach depends on your specific use case and performance requirements. The `object.keys()` method is generally a good choice for most use cases, while traditional `for in` loop or custom iterators may be necessary for more complex scenarios.

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):