Why Is Typeof X Never 'number' When X Comes From The Prompt Function?

I'm having trouble getting the first function (below) to work correctly. I want it to ask for the age of the user with two possible outcomes. If the user enters the correct value (

Solution 1:

As mentioned in the comments, the prompt() function always captures the input as a string, even when the input is a valid number. To check if it's a number, you can try to parse the returned string with parseInt(age_entered) (or parseFloat if you want to allow non-integer ages, although that'd seem odd to me), and if you get back a number, the input is good - if you get back NaN, it wasn't valid.

Here's your script updated based on this understanding:

functionage_of_user() {
    let age_entered = parseInt(prompt("Enter Your Age:")); 
    while (Number.isNaN(age_entered) || age_entered <= 0) {
       alert("You entered an incorrect value. Please enter correct age.");
       age_entered = parseInt(prompt("Enter Your Age:"));
    }   
return age_entered;
}

functionconfirm_age() {
    let age = age_of_user();
    if (age < 18) {
        alert("Sorry! You need to be an adult to view content.");
    }
    else {
        alert("Welcome to our site.");
    }
}

confirm_age();

Solution 2:

The other answers are showing you that prompt() (almost) always returns a string. You'll need to parseInt the response before you can check it for your age range. But I think your while-loop conditional is throwing you off. Also you need to parseInt() on the prompt a second time, inside your while loop. Try it like this:

let age_entered = prompt("Enter Your Age:");
age_entered = parseInt(age_entered); 

while (age_entered <= 0 || Number.isNaN(age_entered)) {
   alert("You entered an incorrect value. Please enter correct age.");
   age_entered = prompt("Enter Your Age:");
   // do parseInt again
   age_entered = parseInt(age_entered); 
}

Notice we use Number.isNaN(age_entered). This is a more robust way to determine if a value is a number than comparing with typeof. See this doc here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/isNaN

Solution 3:

prompt() is always returning a string,

Try parseInt(prompt("Enter Your Age:")).

Solution 4:

It's returning a string, and parseInt will save you:

... 
  let age = parseInt(age_of_user());    
...