How Can I Efficiently Find the Intersection, Difference, and Symmetric Difference of Two JavaScript Arrays?

Finding Array Differences in JavaScript: Intersection, Difference, and Symmetric Difference

In JavaScript, comparing arrays element-by-element can be tedious. To simplify this process, let's explore a powerful tool: Array.prototype.includes().

Intersection

To obtain the values that are common to both arrays, we can use filter(). For instance:

let intersection = arr1.filter(x => arr2.includes(x));

This produces the intersection: [2, 3].

Difference

To identify values present only in arr1, we can filter out the elements that exist in arr2.

let difference = arr1.filter(x => !arr2.includes(x));

This results in the difference: [1].

Symmetric Difference

To get the elements found exclusively in either arr1 or arr2, we combine the two differences:

let symDifference = arr1.filter(x => !arr2.includes(x))
                        .concat(arr2.filter(x => !arr1.includes(x)));

This produces the symmetric difference: [1].

As highlighted by @Joshaven Potter, these methods can be added directly to the Array.prototype for enhanced flexibility:

Array.prototype.diff = function(arr2) { 
  return this.filter(x => !arr2.includes(x)); 
}

Then, you can use it directly on arrays:

[1, 2, 3].diff([2, 3]) // [1]

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