Benchmark: for in vs Object.keys sort

Script Preparation code:



const alpha = 'abcdefghijklmnopqrstuvwxyz';
const keys = [];

for( let i = 0; i < alpha.length; i++ ) {
  for( let j = 0; j < alpha.length; j++ ) {
    for( let k = 0; k < alpha.length; k++ ) {
  		keys.push( alpha[ i ] + alpha[ j ] + alpha[ k ] );
    }
  }
}

function shuffle(array) {
  let currentIndex = array.length,  randomIndex;

  // While there remain elements to shuffle...
  while (currentIndex != 0) {

    // Pick a remaining element...
    randomIndex = Math.floor(Math.random() * currentIndex);
    currentIndex--;

    // And swap it with the current element.
    [array[currentIndex], array[randomIndex]] = [
      array[randomIndex], array[currentIndex]];
  }

  return array;
}

function fill( obj ) {
  shuffle( keys ).forEach( key => {
    obj[ key ] = key;
  } );
  return obj;
}

Tests:

for in
const obj1 = fill( {} ); const obj2 = fill( {} ); let matches = 0; for( const key in obj1 ) { if( obj1[ key ] === obj2[ key ] ) matches++; } console.log( matches );
Object keys sorted
const obj1 = fill( {} ); const obj2 = fill( {} ); const obj1Keys = Object.keys( obj1 ).sort(); const obj2Keys = Object.keys( obj2 ).sort(); const numKeys = obj1Keys.length; let matches = 0; for( let i = 0; i < numKeys; i++ ) { if( obj1[ obj1Keys[ i ] ] === obj2[ obj2Keys[ i ] ] ) matches++; } console.log( matches );

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
for in
Object keys sorted

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):

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Let's break down the benchmark and explain what's being tested, compared, and considered.

**Benchmark Overview**

The benchmark measures the performance of two approaches for iterating over an object in JavaScript: `for...in` loop and using the `Object.keys()` method with sorting. The benchmark generates a large number of objects with random keys and values, shuffles them, and then compares the contents of each object to determine if they match.

**Comparison Options**

The benchmark compares two approaches:

1. **For...in Loop**: This approach uses a traditional `for...in` loop to iterate over the object's properties.
2. **Object.keys() with Sorting**: This approach uses the `Object.keys()` method to get an array of the object's property names, sorts it, and then iterates over the sorted array using another `for...in` loop.

**Pros and Cons**

**For...in Loop:**

* Pros:
	+ Generally faster than `Object.keys()` with sorting due to its native optimization.
	+ Can be more efficient for small objects or when iteration is only needed once.
* Cons:
	+ Less predictable behavior due to the dynamic nature of the `for...in` loop.
	+ May require additional work to ensure accurate matching, especially if the object's structure changes.

**Object.keys() with Sorting:**

* Pros:
	+ More predictable and consistent behavior due to the deterministic nature of sorting.
	+ Easier to reason about and debug, as the iteration order is explicit.
* Cons:
	+ Generally slower than the `for...in` loop due to the overhead of sorting.
	+ May require more memory allocation for the sorted array.

**Other Considerations**

The benchmark uses a library called `shuffle()` to randomize the object's property names. This library is not a built-in JavaScript function, but rather a custom implementation that shuffles an array in place.

Additionally, the benchmark assumes that the object's values are comparable (i.e., can be compared using `===`). If this assumption does not hold for the specific use case, the comparison may produce incorrect results or errors.

**Alternatives**

Other alternatives to these two approaches include:

* Using `Object.entries()` and iterating over the array of key-value pairs.
* Utilizing a data structure like a hash table or trie for faster lookups.
* Implementing a custom iterator using a `for...of` loop or a recursive function.

However, the `for...in` loop and `Object.keys() with Sorting` approaches are commonly used in JavaScript due to their simplicity and performance characteristics.

Related benchmarks:

for in vs Object.keys sort (version: 0)

Comparing performance of: for in vs Object keys sorted

Created: 4 years ago by: Registered User

Jump to the latest result

for in

Object keys sorted

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):