Question 224638 in Javascript Question posted in
A very good W3school tutorial can be found here.

Javascript – user must input a number NOT a letter or special character

I cannot seem to figure this out, very new to JavaScript. I’ve tried isNaN and typeof maybe I’m just writing the if statements wrong.

This is the code I have

// prompt user to select password length, and what characters to include
function promptUser() {
  var passwordLength = parseInt(prompt('How many characters would you like your password length to contain?'));
  
// is length is not a number return null,
  if (passwordLength = isNaN) {
    alert('Password length must be a number.');
    return null;
  }
// password length must be greater than 8
  if (passwordLength < 8) {
    alert('Password length needs to be at least 8 characters in length');
    return null;
  }
 // length must be less than 128
  if (passwordLength > 128) {
    alert('Password length cannot exceed 128 characters in length.');
    return null;
}

I was expecting the

if (passwordlength == //(or === tried both)// isNaN)

to check if it is a number or not but it only spits out alert('Password length must be a number.'); and ignores the return null; no matter what is entered.

Tags:

3

Answers


  1. 0

    You are Setting your passwordLength to isNan every time:

    if (passwordLength = isNaN) {
    alert('Password length must be a number.');
    return null;
  }

    Use:

    if isNaN(passwordLength)  {
    alert('Password length must be a number.');
    return null;
  }

    A single Equals = is a assignment operator and not a comparative operator.

    Therefore your Code will go into this IF statement every time.

    Please change this to a ==, or === for this code to run better.

    Here is some reading on the topic for you: https://www.w3schools.com/js/js_comparisons.asp

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  2. 0

    This part if (passwordLength = isNaN) contains a typo. the "equal to" comparison operator is ‘==’ or ‘===’ (strictly equal).

    Also you should compare it with null, not isNaN.

    Assuming that you are using HTML for input, you will be way better off to use the <input type="number"*gt; and set the minimum and maximum values.

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  3. 0

    You may be using isNaN wrong. Try isNaN(passwordLength) instead. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/isNaN

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