Generating unique random numbers (integers) between 0 and ‘x’

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Use the basic Math methods:

  • Math.random() returns a random number between 0 and 1 (including 0, excluding 1).
  • Multiply this number by the highest desired number (e.g. 10)

  • Round this number downward to its nearest integer

    Math.floor(Math.random()*10) + 1

Example:

//Example, including customisable intervals [lower_bound, upper_bound)
var limit = 10,
    amount = 3,
    lower_bound = 1,
    upper_bound = 10,
    unique_random_numbers = [];

if (amount > limit) limit = amount; //Infinite loop if you want more unique
                                    //Natural numbers than exist in a
                                    // given range
while (unique_random_numbers.length < limit) {
    var random_number = Math.floor(Math.random()*(upper_bound - lower_bound) + lower_bound);
    if (unique_random_numbers.indexOf(random_number) == -1) { 
        // Yay! new random number
        unique_random_numbers.push( random_number );
    }
}
// unique_random_numbers is an array containing 3 unique numbers in the given range

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