Let's break down the JavaScript microbenchmark provided by MeasureThat.net.

Benchmark Definition

The benchmark definition is a JSON object that describes two test cases: "map + set" and "set + array.from + map". These test cases are designed to measure the performance of creating a Set data structure from an array using different approaches.

Script Preparation Code

The script preparation code generates a large array of 10,000 random integers:

var array = [];
for (let i = 0; i < 10000; i++) {
  array.push(Math.round(Math.random() * 100));
}

This array will be used to test the performance of creating a Set data structure from it.

Html Preparation Code

The html preparation code is empty, which means that no HTML markup is provided for the benchmark.

Test Cases

There are two test cases:

1. map + set

const set = new Set();
array.map((item) => {
  if (set.has(item)) {
    set.add(item);
    return item;
  }
}).forEach(item => set.add(item));

In this approach, an existing Set is created and then the map() method is used to iterate over the array. If an element is already present in the Set, it is added to the Set using set.add(). The elements that are not present in the Set are returned by the map() callback function.

2. set + array.from + map

const set = new Set(array);
Array.from(set).map((item) => {
  return item;
});

In this approach, a new Set is created directly from the array using arrayFrom() method and then the map() method is used to iterate over the Set. The elements that are not present in the Set are returned by the map() callback function.

Library and Purpose

Both test cases use the built-in JavaScript Set data structure, which is implemented as a hash table. The Set data structure provides fast membership testing (i.e., checking if an element is already present in the set) and efficient insertion of new elements.

Pros and Cons

Here are some pros and cons of each approach:

1. map + set
   • Pros:
     • Can be more memory-efficient, as it avoids creating a temporary array using arrayFrom().
     • May perform better for small arrays or arrays with frequent membership testing.
   • Cons:
     • Requires iterating over the array twice (once to create the Set and once to iterate over its elements).
     • May require more CPU cycles due to the nested iteration.
2. set + array.from + map
   • Pros:
     • Creates a new Set directly from the array, which can be faster than creating an empty Set and then adding all elements using add().
     • Uses a single pass over the array, which can reduce CPU cycles.
   • Cons:
     • Creates a temporary array using arrayFrom(), which may consume more memory.
     • May perform slower for very large arrays or arrays with infrequent membership testing.

Special JS Features and Syntax

There are no special JavaScript features or syntax used in these test cases. Both approaches use standard JavaScript syntax to create the Set data structure and iterate over its elements.

Alternatives

If you need to compare performance of creating a Set data structure from an array, here are some alternative approaches:

1. Using reduce() method: You can use the reduce() method to create a new Set by iterating over the array:

const set = array.reduce((acc, item) => {
  if (!acc.has(item)) {
    acc.add(item);
  }
  return acc;
}, new Set());

This approach is similar to using map(), but uses a single pass over the array and avoids creating a temporary array.

2. Using a custom function: You can write a custom function to create a Set data structure from an array:

function createSet(array) {
  const set = new Set();
  for (const item of array) {
    if (!set.has(item)) {
      set.add(item);
    }
  }
  return set;
}

// Usage:
const set = createSet(array);

This approach provides more control over the creation process, but may require more CPU cycles due to the custom function.