Question

I’m running some functions to verify that the user-entered text in a form contains at least one number and letter. It doesn’t seem to be working. Since the two functions are nearly identical, I’ll just post one of them:

function hasALetter(textField){
    //returns true or false based on whether or not the text field has at least one letter inside it    
    console.log("Checking for letters...");

    var hasLetter = false;

    for(var i=0, checkLength=textField.length; i<checkLength; i++){
        var letter = textField.substr(i,1);
        console.log("letter = " + letter);
        if(isNan(letter) == false){
            hasLetter = false;
        }
    }
    if(hasLetter == true){
        return true;
    }
}

The log (“letter = ” + letter) never shows up in my console. I’m probably missing something silly, but it doesn’t seem to be completing the function.

For reference, here is how I’m calling the functions:

if(pwd.value.length > 9){

            var pwdLetter = hasALetter(pwd);
            var pwdNumber = hasADigit(pwd);

            if(pwdLetter==true){
                if(pwdNumber==true){

Yes, I’m aware that it’s very messy, but I’m still learning. I’m sure there’s more advanced/cleaner ways of doing this validation, but for the purposes of my schooling, I’m doing it like this for now.

Answer 1

The easiest way to check if a string has a letter is the Regular Expression:

function hasLetter(str){
  // check for characters between a and z
  // i flag makes it case insensitive
  return /[a-z]/i.test(str);
}

If you want to loop through the string and also want to use the isNaN function, this would do:

function hasLetter(str){

  // loop through every character
  for(var i=0; i<str.length; i++){

    // check if the i-th character is not a number
    if(isNaN(str[i])){

      // if so, return true
      return true;
    }
  }

  // if the loop has finished and no letters have been found, return false
  return false;
}

But I would not recommend this method, because isNaN checks whether the first argument is a number or not. First of all, not all characters that aren’t numbers are letters. Secondly, the argument you pass in is a string (str[i] returns a character of type string, even if it is a digit)