Tips on obtaining user input through prompt for verifying if a number within a while loop

Question

Tips on obtaining user input through prompt for verifying if a number within a while loop

I am a beginner at javascript and I have been searching everywhere for an answer on how to validate user input from a prompt to ensure the correct number is entered. I've tried result!==isNan(), result==isNan(Nan), and various other variations. Can someone please explain why this isn't working and provide guidance on how to make it work?


var result = prompt("Enter a number between 4-10"); 
    while (result<4 || result>10 || result==isNaN(result)) {
        var result = prompt("Please enter a number between 4-10!");
    }
  alert ("Success")

javascript while-loop nan prompt

Answer 1

Answer №1

To determine if the result is valid, you can use the following code: isNan(result) == true

<script>
var result = prompt("Please enter a number between 4 and 10"); 
while (result < 4 || result > 10 || isNaN(result) == true) {
    var result = prompt("You must enter a number between 4 and 10!");
}
alert ("Success")
</script>

Answer 2

To determine if the result is valid, you can use the following code: isNan(result) == true

<script>
var result = prompt("Please enter a number between 4 and 10"); 
while (result < 4 || result > 10 || isNaN(result) == true) {
    var result = prompt("You must enter a number between 4 and 10!");
}
alert ("Success")
</script>

Answer 3

Answer №2

The code result==isNaN(result) is not being executed at all

// When using prompt, values returned are strings or null (if cancelled)
// Comparing with a number will convert values to numbers automatically
console.log(Number(null)) // 0
console.log(Number('5')) // 5
console.log(Number('')) // 0

// Due to the condition result<4 || result>10 evaluating to true for null and '', isNaN() code is never reached, leading to an endless loop.

var result = prompt("Enter a number between 4-10"); 
while (result<4 || result>10) {
  result = prompt("Please enter a number between 4-10!");
  if (result === null) break;
}
alert(`Success: ${result}`)

Consider using recursion in place of the while loop

askUser();

function askUser(){
  let answer = prompt('Hello! Please input a number between 4 and 10:');
  if (answer > 4 && answer < 10)
    alert('Thank you, you're awesome!')
  else if (answer === null)
    alert('Seriously? You can't think of a number between 4 and 10??!?!?')
  else 
    askUserAgain();
}

function askUserAgain() {
  let answer = prompt('The entered value is not between 4 and 10, try again.');
  if (answer > 4 && answer < 10)
    alert('Thank you, you're awesome!')
  else if (answer === null)
    alert('Seriously? You can't think of a number between 4 and 10??!?!?')
  else 
    askUserAgain();
}

Answer 4

The code result==isNaN(result) is not being executed at all

// When using prompt, values returned are strings or null (if cancelled)
// Comparing with a number will convert values to numbers automatically
console.log(Number(null)) // 0
console.log(Number('5')) // 5
console.log(Number('')) // 0

// Due to the condition result<4 || result>10 evaluating to true for null and '', isNaN() code is never reached, leading to an endless loop.

var result = prompt("Enter a number between 4-10"); 
while (result<4 || result>10) {
  result = prompt("Please enter a number between 4-10!");
  if (result === null) break;
}
alert(`Success: ${result}`)

Consider using recursion in place of the while loop

askUser();

function askUser(){
  let answer = prompt('Hello! Please input a number between 4 and 10:');
  if (answer > 4 && answer < 10)
    alert('Thank you, you're awesome!')
  else if (answer === null)
    alert('Seriously? You can't think of a number between 4 and 10??!?!?')
  else 
    askUserAgain();
}

function askUserAgain() {
  let answer = prompt('The entered value is not between 4 and 10, try again.');
  if (answer > 4 && answer < 10)
    alert('Thank you, you're awesome!')
  else if (answer === null)
    alert('Seriously? You can't think of a number between 4 and 10??!?!?')
  else 
    askUserAgain();
}

Tips on obtaining user input through prompt for verifying if a number within a while loop

Answer №1

Answer №2

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