How to shuffle an array

In a small talk, one of my friends asked me, without searching or using AI, can you figure out how to shuffle an array in JavaScript?

Surprisingly, I couldn’t answer him immediately. I was thinking about the sort method, but I couldn’t remember the exact implementation, and I even thought about using timestamp as seed to generate a random number.

After the talk, I figured out the answer in a very short time. Here is the code:

const shuffle = (arr) => arr.sort(() => Math.random() - 0.5);

Fine, this code is written by AI and its so simple and obvious. And here is the code that I want to write:

const shuffle = (arr) => {
    const len = arr.length;
    for (let i = 0; i < len; i++) {
        const randomIdx = Math.floor(Math.random() * len);
        [arr[i], arr[randomIdx]] = [arr[randomIdx], arr[i]];
    }
    return arr;
}

And then AI tells me about the Fisher-Yates shuffle algorithm, which is the most efficient way to shuffle an array. Here is the code:

const shuffleFisherYates = (arr) => {
  for (let i = arr.length - 1; i > 0; i--) {
    const randomIdx = Math.floor(Math.random() * (i + 1));
    [arr[i], arr[randomIdx]] = [arr[randomIdx], arr[i]];
  }
  return arr;
}

why it is more effective? Because

• compare with using sort function, it only needs to iterate through the array once, while the sort method may iterate multiple times
• compare with my implementation, mine always generates a random number which from 0 to the length of the array, while Fisher-Yates shuffle algorithm only generates a random number which from 0 to the current index of the array.
• compare with my implementation, mine always swaps the element with itself, while Fisher-Yates shuffle algorithm only swaps the element with the element that has not been swapped.

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