JavaScript Only Return random number which is not in array

I want to make a function that takes an array as an argument, creates a random number from 1 - 10, and runs until it creates a number that is not in the array, and returns it.

Here is jsfiddle

function contains() {
  var check = false;
  while (!check) {
    var random = Math.floor(Math.random() * 10);
    random += 1;
    for (var i = 0; i < arr.length; i++) {
      if (arr[i] === random) {
        console.log(random);
        check = false;
        return false;
      }
    }
    check = true;
    console.log(random);
    return true;
  }
}

var arr = [1, 2, 3, 4, 5, 6];

$(".test").on("click", function() {
  contains(arr);
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<button class="test">
Test
</button>
Answer:1

Multiple mistakes

  • arr that is being used by contains function is localized when you passed the same as an argument. contains function is not able to access the global arr

  • You are returning both true and false, so even if the random item is included in the arr, contains return from the function.

Make it

function contains() {
  var check = false;
  while (!check) {
    var random = Math.floor(Math.random() * 10);
    check = !arr.includes(random);
  }
  return random;
}

Demo

function contains() {
  var check = false;
  while (!check) {
    var random = Math.floor(Math.random() * 10);
    check = !arr.includes(random);
  }
  return random;
}

var arr = [1, 2, 3, 4, 5, 6];

$(".test").on("click", function() {
  console.log(contains());
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>


<button class="test">
Test
</button>
Answer:2

You could use a do ... while loop, because you need at least one loop for checking the random number, and check with Array#includes for continuing the loop.

Don't forget to hand over the array for checking and use that array inside of the function.

function contains(array) {
    var random;
    
    do {
        random = Math.floor(Math.random() * 10) + 1;
    } while (array.includes(random))

    return random;
}

var numbers = [1, 2, 3, 4, 5, 6];

console.log(contains(numbers));
Answer:3

I have proposed the solution with the use of indexOf()

var arr = [1, 2, 3, 4, 5, 6];

function contains() {
  var randomNumber = Math.floor((Math.random() * 10) + 1);
  if (arr.indexOf(randomNumber) === -1) {
    return randomNumber;
  } else {
    console.log(`Number exists: ${randomNumber}`);
  }
}

$(".test").on("click", function() {
  var returnNumber = contains();
  if (!!returnNumber) {
    console.log(`Number not exists: ${returnNumber}`);
  }
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<button class="test">
Test
</button>
Answer:4

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