[TS] Swap two element in the array (mutation)

Shuffling is a common process used with randomizing the order for a deck of cards. The key property for a perfect shuffle is that each item should have an equal probability to end up in any given index.

In this lesson we discuss the concept behind the simple modern fisher yates shuffle and implement it in JavaScript / TypeScript.

 

function randomInt(start: number, before: number) {
  return start + Math.floor(Math.random() * (before - start));
}

 function shuffle<T>(array: T[]): T[] {
  array = array.slice();

  for (let i = 0; i < array.length; i++) {
    const randomChoiceIndex = randomInt(i, array.length);
    [array[i], array[randomChoiceIndex]] = [array[randomChoiceIndex], array[i]]; // swap element in array
  }

  return array;
}