A Common-Sense Guide to Data Structures and Algorithms in JavaScript, Volume 1

A Practical Example

Suppose you’re writing a JavaScript application, and somewhere in your code you find that you need to get the intersection between two arrays. The intersection is a list of all the values that occur in both of the arrays. For example, if you have the arrays [3, 1, 4, 2] and [4, 5, 3, 6], the intersection would be a third array [3, 4] since both of those values are common to the two arrays.

Here’s one possible implementation:

function intersection(firstArray, secondArray) {
  const result = [];

  for (const i of firstArray) {
    for (const j of secondArray) {
      if (i === j) {
        result.push(i);
      }
    }
  }

  return result;
}

Here, we’re running nested loops. In the outer loop, we iterate over each value ...