How to Generate Non-Repeating Random Numbers in JavaScript without Recursion?

Generating Non-Repeating Random Numbers in JavaScript

Generating a sequence of non-repeating random numbers can be a challenge in JavaScript. Here's a breakdown of a representative problem and its resolution.

The Problem:

The provided code attempts to generate non-repeating random numbers by checking against an array of previously generated numbers. However, this approach triggers a stack overflow error due to recursive function calls.

The Best Solution:

Instead of continuous recursive function calls, consider generating a shuffled array of numbers at the outset. This approach ensures that each number is generated only once. Here's a Fisher–Yates Shuffle that achieves this efficiently:

<code class="javascript">function shuffle(array) {
  let i = array.length;
  let j = 0;
  let temp;

  while (i--) {
    j = Math.floor(Math.random() * (i + 1));
    temp = array[i];
    array[i] = array[j];
    array[j] = temp;
  }

  return array;
}

let ranNums = shuffle([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]);</code>

This technique avoids costly array operations by swapping elements directly within the original array.

Another Alternative:

For browsers with generator support, you can use the following generator function:

<code class="javascript">function* shuffle(array) {
  let i = array.length;

  while (i--) {
    yield array.splice(Math.floor(Math.random() * (i + 1)), 1)[0];
  }
}

let ranNums = shuffle([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]);

ranNums.next().value; // first random number from array
ranNums.next().value; // second random number from array
// etc.</code>

By utilizing yielded values, this approach delays array operations until they are actually required, making it more efficient for certain use cases. Whichever method you choose, these solutions effectively generate non-repeating random numbers in JavaScript.

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