The benchmark defined tests the performance differences between using JavaScript objects and the Map data structure. Specifically, it examines how well these structures perform when inserting a series of key-value pairs in different formats.

Test Cases Comparison

1. Test Name: "Obj / Object.entries()"

   • Benchmark Definition:

     let obj = {};
     for (let i = 0; i < 100000; i++) {
       obj[i] = i;
     }
     

   • Description: This test creates a plain JavaScript object and populates it with 100,000 key-value pairs, where both the keys and values are the integers from 0 to 99,999. The benchmark likely measures Object.entries() at a later stage, as it retrieves the entries from the object.

   • Pros:

     • Simple and widely used data structure.
     • Fast property access (obj[i]).

   • Cons:

     • Not ordered; the keys are not guaranteed to maintain a specific order.
     • Non-integer keys are coerced to strings.
     • Performance can degrade with a large number of properties.

2. Test Name: "Map / spread"

   • Benchmark Definition:

     let map = new Map();
     for (let i = 0; i < 100000; i++) {
       map.set(i, i);
     }
     

   • Description: This test uses the Map object, which is a collection of key-value pairs, where both keys and values can be of any type. The benchmark likely uses the spread syntax to analyze the performance of creating an array from the map.

   • Pros:

     • Maintains the insertion order of keys.
     • Can use objects as keys, making it more versatile.
     • Better performance for frequent additions/deletions.

   • Cons:

     • More memory consumption compared to plain objects.
     • Slightly slower access time for primitives compared to objects due to overhead.

3. Test Name: "Map / Array.from()"

   • Benchmark Definition:

     let map = new Map();
     for (let i = 0; i < 100000; i++) {
       map.set(i, i);
     }
     

   • Description: This scenario, like the previous Map test, explores using Array.from() to convert the entries of the Map into an array.

   • Pros & Cons: Similar to the "Map / spread" test.

     • The use of Array.from() allows for flexible transformations but may come with performance overhead compared to the spread syntax depending on the context.

Performance Results

From the benchmark results provided, we can analyze how each approach performed in terms of executions per second on the same machine/browser environment.

• Obj / Object.entries(): 1494.59 executions/second
• Map / Array.from(): 235.50 executions/second
• Map / spread: 233.85 executions/second

The object approach significantly outperformed the Map approaches, demonstrating that for straightforward key-value storage, especially when using integer keys, objects are more efficient. However, the differences in performance for Map are relatively minor between the two methods of conversion to an array, indicating that either method can be used depending on the developer's preference or specific use case.

Alternatives

1. WeakMap and WeakSet: These provide a way to create key-value pairs where keys are weakly referenced, meaning they do not prevent garbage collection if there are no other references to the key.

2. Set: While not strictly a key-value pair structure, a Set can be used to store unique values and has interesting performance characteristics.

3. Immutable data structures: Libraries like Immutable.js provide structures that can be more performant for certain types of operations, especially when dealing with large amounts of data that require frequent state changes.

By choosing the right data structure, developers can optimize their applications based on specific needs for performance, memory usage, or ordering behavior.