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My variable starts with 'undefined' followed by the variable when viewed in HTML

so I am making a converter from Decimal to Binary using JS and HTML. I’m nearly finished with my task, but my code keeps printing ‘undefined‘ along with the answer.

For example, if I enter the number 9, I will get an output of:

0bundefined1001

Why is the ‘undefined’ there, and how do I get rid of it?

// NECESSARY VARIABLES DEFINED
let decimalNum; // User's input
let binaryNum; // (soon) converted decimalNum
let x = 0; // explained in the algorithm 

// THIS FUNCTION CHECKS WHETHER THE USER'S INPUT IS A NATURAL NUMBER
function is_Natural(n) {
  if (typeof n !== 'number')
    return 'Not a number';
  return (n > 0) && (Math.floor(n) === n) && n !== Infinity;
}

// THIS SECTION CONVERTS THE USER'S INPUT TO THE BINARY SYSTEM
document.getElementById("mySubmit").onclick = function() {
  decimalNum = document.getElementById("decimalNum").value; //retrieves the user's input and stores it in the previously defined variable
  decimalNum = Number(decimalNum)
  if (is_Natural(decimalNum) === true) {
    while (true) {
      if (decimalNum < 2 ** x) {
        x = x - 1 // For it to let the left-most value be equal to 1
        break
      } else {
        x = x + 1
      }
    }
    while (true) {
      if (decimalNum >= 2 ** x) {
        binaryNum = binaryNum + '1';
        decimalNum = decimalNum - 2 ** x;
        x = x - 1
      } else {
        binaryNum = binaryNum + '0'
        x = x - 1
      }
      if (x < 0) {
        break
      } else {
        continue
      }
    }
  }
  document.getElementById("binaryNum").textContent = `Here is your number in the Binary system: 0b${binaryNum}`; // replaces the placeholder
}
<h1> Converter from Decimal to Binary</h1>
<label for="decimalNum" title="A positive whole number (1, 2, 3, etc.), excluding 0 and inifinity."> Decimal (natural number) </div>: </label>
<input id="decimalNum" type="number">
<button id="mySubmit"> Submit </button>
<p id="binaryNum"> </p>
<!-- Placeholder for the printed form in the Binary system.-->
<i> Please note that the <b>0b</b> index in the Binary number is a prefix to indicate its system.</i>
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2

Answers


  1. 0

    the binaryNum variable without initializing it with an empty string. as an output it starts with the undefined (the default value for an uninitialized variable in JavaScript for let,var).

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  2. 0

    ‘binaryNum’ requires a default value

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