Why not unique numbers are still coming?

I need to generate the unique numbers, join it with the letter and push to array.

arr = []
for (var i = 0; i < 5; i++) {
  function generateRandomNumber(min, max) {
    return Math.floor(Math.random() * (max - min + 1) + min);
  }
  var randomNum = generateRandomNumber(1, 15);
  if (!arr.includes(randomNum)) {
    arr.push('B' + randomNum.toString())
  } else {
    if (arr.length < 5) {
      return generateRandomNumber(min, max)
    } else break
  }
}

I have provisioned uniqueness check, however the same values are still coming.

> I have provisioned uniqueness check, however the same values are still coming.

The uniqueness check is incorrect.<br>
The array contains only strings starting with letter 'B' (added by the line arr.push('B' + randomNum.toString())) while the uniqueness check searches for numbers.

The call arr.includes(randomNum) always returns false. Each and every generated value of randomNum is prefixed with 'B' and pushed into the array, no matter what the array contains.

Try a simpler approach: generate numbers, add them to the list if they are not already there, stop when the list is large enough (five items).<br>
Then run through the list and add the 'B' prefix to each item.

Like this:

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

function generateRandomNumber(min, max) {
  return Math.floor(Math.random() * (max - min + 1) + min);
}


// Generate 5 unique random numbers between 1 and 15
let arr = []
while (arr.length < 5) {
  let num = generateRandomNumber(1, 15);
  // Ignore a value that has already been generated
  if (!arr.includes(num)) {
    arr.push(num);
  }
}

// Add the 'B' prefix to the generated numbers
arr = arr.map((num) => `B${num}`);

console.log(arr);

<!-- end snippet -->

Condition only checked once in the loop.
Also if the condition is in the else state, there is a chance that there will also be same number as previous.
You can use this approach

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

let arr = []
function generateRandomNumber(min, max) {
    return Math.floor(Math.random() * (max - min + 1) + min);
}

function add(){
  var randomNum = generateRandomNumber(1, 15);
    if(arr.length < 5){
        if (!arr.includes('B' + randomNum.toString())) {
            arr.push('B' + randomNum.toString())
        }
        add()
    }
  
}
add()
console.log(arr)

<!-- end snippet -->