JavaScript - Continuously ask for input until a number is entered

Question

JavaScript - Continuously ask for input until a number is entered

I am attempting to create a loop that asks the user for a number until they input an actual number, triggering an alert box each time.

Despite using a while loop and `isNaN`, my current implementation seems to be flawed.

This is the JavaScript code I have so far:

var correct = false;

do {
    var question = prompt("Guess the number?");
    if (question !== isNaN) {
        document.write("Your number is " + question);
        correct = true;
        break;
    }

} while (!correct);

javascript loops

Answer 1

Answer №1

A few errors to avoid

isNaN() functions as follows: isNaN(NaN) will result in true, while isNaN(1) or isNaN("1") will result in false
prompt() always provides a string, never NaN

To convert the prompt() output into a number, you can utilize the unary + operator and then check if it is NaN;

var question = prompt("guess the number?");
if (!isNaN(+question)) {
  ...

However, if you simply need to determine whether a string consists solely of numbers, isNaN() may not be suitable, as whitespace ("", " ", or "\n\t") all convert to 0 causing false positives.

For this purpose, utilizing a basic regex pattern would be more appropriate;

var question = prompt("guess the number?");
var containsOnlyDigits = /^[0-9]+$/; // one or more of digits 0 to 9
if (containsOnlyDigits.test(question)) {
  ...

Answer 2

A few errors to avoid

isNaN() functions as follows: isNaN(NaN) will result in true, while isNaN(1) or isNaN("1") will result in false
prompt() always provides a string, never NaN

To convert the prompt() output into a number, you can utilize the unary + operator and then check if it is NaN;

var question = prompt("guess the number?");
if (!isNaN(+question)) {
  ...

However, if you simply need to determine whether a string consists solely of numbers, isNaN() may not be suitable, as whitespace ("", " ", or "\n\t") all convert to 0 causing false positives.

For this purpose, utilizing a basic regex pattern would be more appropriate;

var question = prompt("guess the number?");
var containsOnlyDigits = /^[0-9]+$/; // one or more of digits 0 to 9
if (containsOnlyDigits.test(question)) {
  ...

Answer 3

Answer №2

Check out these helpful tips using the code example below:

<html>
 <head>
    <title></title>
    <script>

    var userAnswer = "";

    do {
        userAnswer = prompt("Guess the number?");
    } while(!isNumber(userAnswer));

    document.write("Your number is " + userAnswer);

    function isNumber(value) {
      var numberPattern = /^[0-9]+$/; // one or more of digits 0 to 9
      return numberPattern.test(value);
    }

    </script>
 </head>
 <body>

</body>

See an example here: https://plnkr.co/edit/ziysG36if9OTZahHfSbO

Avoid creating unnecessary variables like 'correct' to check true or false conditions. Use the clear condition 'isNaN(answer)' directly in the while loop.
Keep your code clean and understandable. It's clearer to name the variable storing the prompt result as "userAnswer" instead of something misleading like "answer".

Answer 4

Check out these helpful tips using the code example below:

<html>
 <head>
    <title></title>
    <script>

    var userAnswer = "";

    do {
        userAnswer = prompt("Guess the number?");
    } while(!isNumber(userAnswer));

    document.write("Your number is " + userAnswer);

    function isNumber(value) {
      var numberPattern = /^[0-9]+$/; // one or more of digits 0 to 9
      return numberPattern.test(value);
    }

    </script>
 </head>
 <body>

</body>

See an example here: https://plnkr.co/edit/ziysG36if9OTZahHfSbO

Avoid creating unnecessary variables like 'correct' to check true or false conditions. Use the clear condition 'isNaN(answer)' directly in the while loop.
Keep your code clean and understandable. It's clearer to name the variable storing the prompt result as "userAnswer" instead of something misleading like "answer".

Answer 5

Answer №3

isNan is not just a word - it's actually a function that you have to remember to call! You do this by adding parentheses after the function name and then placing your arguments inside those parentheses.

When you use the isNaN function, it will give you a true result if the argument you passed in is not a number, and a false result if it is indeed a number. In this case, we are checking whether the variable question contains a numerical value. By using the exclamation mark ! before the condition, we can reverse the boolean output, so that the statement within the if block will execute only if question is a number.

var correct = false;

do {
  var question = prompt("Can you guess the number?");
  if (!isNaN(question)) {
    document.write("The number you entered is: " + question);
    correct = true;
    break;
  }
} while (!correct);

Answer 6

isNan is not just a word - it's actually a function that you have to remember to call! You do this by adding parentheses after the function name and then placing your arguments inside those parentheses.

When you use the isNaN function, it will give you a true result if the argument you passed in is not a number, and a false result if it is indeed a number. In this case, we are checking whether the variable question contains a numerical value. By using the exclamation mark ! before the condition, we can reverse the boolean output, so that the statement within the if block will execute only if question is a number.

var correct = false;

do {
  var question = prompt("Can you guess the number?");
  if (!isNaN(question)) {
    document.write("The number you entered is: " + question);
    correct = true;
    break;
  }
} while (!correct);

Answer 7

Answer №4

isNaN is a unique function that follows specific rules. It's recommended to convert the input into a number first before using isNaN on the result. If the conversion from a string to a number fails, Number will return NaN.

var input1 = "1234";
var input2 = "abcd";

alert(isNaN(Number(input1)));
alert(isNaN(Number(input2)));

Answer 8

isNaN is a unique function that follows specific rules. It's recommended to convert the input into a number first before using isNaN on the result. If the conversion from a string to a number fails, Number will return NaN.

var input1 = "1234";
var input2 = "abcd";

alert(isNaN(Number(input1)));
alert(isNaN(Number(input2)));

Answer 9

Answer №5

The isNan function mentioned above takes a parameter as input.

There is no need to convert the prompt to a number before testing in the isNan function, as it can accept strings according to the documentation provided.

For more information, visit: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/isNaN#Examples

The function internally handles the conversion process:

You may consider isNaN to be like this:
isNaN = function(value) {
   Number.isNaN(Number(value));
}

Below is a code snippet that may be helpful:

var correct = false;

do {
    var answer = prompt("Guess the number?");

    // The isNaN function requires a numerical argument
    // Also, ensure there is a value present.
    // If the user clicks ESC or cancels, null will be returned
    if (answer && !isNaN(answer)) {

        // Writing to the document is not possible after it has loaded
        // This action will clear any existing content on the page
        document.write("Your number is " + answer);
        correct = true;
        break;
    }

} while (!correct);

Answer 10

The isNan function mentioned above takes a parameter as input.

There is no need to convert the prompt to a number before testing in the isNan function, as it can accept strings according to the documentation provided.

For more information, visit: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/isNaN#Examples

The function internally handles the conversion process:

You may consider isNaN to be like this:
isNaN = function(value) {
   Number.isNaN(Number(value));
}

Below is a code snippet that may be helpful:

var correct = false;

do {
    var answer = prompt("Guess the number?");

    // The isNaN function requires a numerical argument
    // Also, ensure there is a value present.
    // If the user clicks ESC or cancels, null will be returned
    if (answer && !isNaN(answer)) {

        // Writing to the document is not possible after it has loaded
        // This action will clear any existing content on the page
        document.write("Your number is " + answer);
        correct = true;
        break;
    }

} while (!correct);

Answer 11

Answer №6

Check out this alternative approach:

let isNumberValid = false;
while (!isNumberValid) {
  let userGuess = prompt("Try to guess the number:", "Number");
  isNumberValid = !isNaN(userGuess);
}
document.write("The number you guessed is: " + userGuess);

Answer 12

Check out this alternative approach:

let isNumberValid = false;
while (!isNumberValid) {
  let userGuess = prompt("Try to guess the number:", "Number");
  isNumberValid = !isNaN(userGuess);
}
document.write("The number you guessed is: " + userGuess);

JavaScript - Continuously ask for input until a number is entered

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

Answer №6

Similar questions

Quoting Properties in Javascript Objects

Creating a binary variable in R for a new column by leveraging the values from an existing column

Error: Unable to import 'index.js' with the require() function in the current directory

Linux web server blocking requests across different domains, even with correct Access-Control-Allow-Origin headers set

Java - RESTful API endpoint that serves images when available and JSON data when images are not available

What is the most effective way to output data using the response.write method in a Node.js program after retrieving it from a MySQL server?

ExpressJS exhibits unique behavior based on whether the API is requested with or without the specified PORT number

Run a series of functions with arguments to be executed sequentially upon the successful completion of an ajax request

Retrieve the specific array element from parsing JSON that includes a particular phrase

The Nextjs framework is experiencing a high total blocking time in its *****.js chunk

Update data dynamically on a div element using AngularJS controller and ng-repeat

Is there a way to update textures for a MTLLoader.MaterialCreator object in three.js?

What is the best way to iterate through a JSON associative array using JavaScript?

What causes a ReferenceError when attempting to retrieve the class name of a React component?

Webpack encounters an error while attempting to load Bootstrap v4.0.0-beta

Connecting Ember controllers with views/elements

After successfully installing an SSL certificate on my nginx server, attempting to access the URL in the browser only results in an error message: ERR_CONNECTION

How to access a specific element within an ng-grid

Exploring Javascript's Timing Functions: SetInterval() and ClearInterval()

Utilizing Three.js to Upload Images and Apply Them as Textures