This benchmark compares two JavaScript approaches to iterating over the properties of an object: using a for...in loop versus using Object.keys() to retrieve an array of the object's keys and then iterating over that array with a traditional for loop.

Tested Options

1. for-in Loop:

   • Test Code:

     let res = 0;
     for (var i = 10000; i > 0; i--) {
       for (var key in obj) {
         res = obj[key];
       }
     }
     

   • Mechanism: The for...in statement iterates over the enumerable properties of an object. In this benchmark, it accesses each property of obj, which contains simple key-value pairs.

2. Object.keys() Method:

   • Test Code:

     let res = 0;
     for (var i = 10000; i > 0; i--) {
       const keys = Object.keys(obj);
       const l = keys.length;
       for (var e = 0; e < l; e++) {
         res = obj[keys[e]];
       }
     }
     

   • Mechanism: The Object.keys() method creates an array of a given object’s own enumerable property names, iterating over that array provides access to the values via the keys.

Pros and Cons

for-in Loop

• Pros:

  • Simplicity: Directly iterates over properties without needing to create an intermediate array.
  • Less memory overhead: No additional array is created.

• Cons:

  • Potentially slower: It may enumerate properties in an order that is platform-dependent and can include inherited enumerable properties, which may slow down execution if additional properties are in the prototype chain.
  • Requires checks with hasOwnProperty if there are inherited properties that should be ignored.

Object.keys()

• Pros:

  • Predictable: By creating an array of keys, it operates only on the object's own properties and ignores inherited properties automatically.
  • Performance: In certain contexts, it might perform better, especially when the object has a large number of properties as it avoids some overhead.

• Cons:

  • Memory Usage: Creating an intermediate array can increase memory usage, potentially impacting performance on memory-constrained environments.
  • Slightly more complex: Two steps are required (fetching keys and then iteration), which can add slight overhead.

Benchmark Results

According to the benchmark results from a specific setup:

• The for-in loop achieved 84.15 executions per second, while the Object.keys() approach achieved 68.66 executions per second.
• This suggests that in this particular test environment and configuration, the for-in loop performed better.

Other Considerations

When choosing between these two methods, developers should evaluate:

• Context: In scenarios where performance is critical, the actual data structure and size can make one method preferable over the other.
• Use Case: If you’re iterating over a large dataset or require predictable behavior with properties, Object.keys() may be the better choice despite slightly higher overhead.
• JavaScript Engine: Execution speed can vary between different JavaScript engines (e.g., Chrome’s V8 vs. Firefox’s SpiderMonkey), making real-world performance testing crucial depending on the target environment.

Alternatives

Other alternatives for iterating over object properties include:

• forEach with Object.entries(): Using Object.entries(obj).forEach() provides an iterator that returns both keys and values but may have overhead for larger objects.
• Map and Set: If the object needs frequent updates or the order of entries matters, switching to a Map may be more effective, as they maintain insertion order and offer methods for easy iteration.

In conclusion, the choice between for...in and Object.keys hinges on the specific requirements of your application, including element properties, performance needs, and readability.