This benchmark compares the performance of different methods for iterating over the properties of an object in JavaScript: the for...in loop versus the Object.keys method.

Benchmark Options

1. for-in Loop

   • Test Case:

     const r = [];
     for (var i = 10000; i > 0; i--) {
       for (var key in getObj(i)) {
         r[i] = key;
       }
     }
     console.log(r.length);
     

2. Object.keys Method

   • Test Case:

     const r = [];
     for (var i = 10000; i > 0; i--) {
       Object.keys(getObj(i)).forEach(key => {
         r[i] = key;
       });
     }
     console.log(r.length);
     

Pros and Cons

for-in Loop

• Pros:

  • Simple syntax that can directly iterate over the enumerable properties of an object.
  • Requires less boilerplate code as you don’t need to create an intermediate array of keys.

• Cons:

  • It also iterates over inherited enumerable properties (from the prototype chain), which can lead to unexpected results if not filtered.
  • Slower performance compared to Object.keys in most environments, as demonstrated by the benchmark results where for-in executed 252.42 operations per second.

Object.keys Method

• Pros:

  • Only iterates over the object's own properties, excluding any properties that might be inherited, providing cleaner and expected results.
  • Generally faster performance due to optimizations in modern JavaScript engines, as indicated by its higher execution rate of 318.13 operations per second in the benchmark.

• Cons:

  • Slightly more complex syntax since it creates an array of keys that you then need to iterate over with a method like forEach, though this is often negligible in practice.

Other Considerations

• Object.values / Object.entries: Additional methods like Object.values() and Object.entries() can be used to retrieve property values or key-value pairs respectively. These methods provide flexibility depending on whether you need keys, values, or both during iteration.

• Iterating Performance: In scenarios where performance is critical (e.g., dealing with a large number of object properties or in performance-sensitive applications), using Object.keys is generally advisable based on this benchmark's results.

• Code Readability: Modern JS development highly values readability. Using Object.keys is often preferred by developers for its clarity about the intent to only iterate over own properties. The functional style of forEach can also be more expressive compared to traditional loops.

Alternatives

In addition to the methods tested, other alternatives for iterating over object properties include:

• Object.values(): If you only need the values of the properties.
• Object.entries(): If both keys and values are needed together.
• forEach with a Map or Set: If you are using collections, these data structures provide methods to iterate over elements with built-in methods.

In summary, this benchmark highlights the performance differences between two common object-property iteration techniques in JavaScript. It suggests that while both methods are valid, Object.keys is generally the more performant and cleaner option for most scenarios.