Problem with my addEventListner returning null in javascript

Hey was wondering if anyone would be able to help me figure out where I went wrong in this code. I am very new to coding so sorry if it is a little wonky. Very open to any feedback! I am trying to make a password generator that prompts you asking how many characters in total and which characters to include.

The function worked when I logged it but adding it to the button to generate when you click it kinda went a little downhill.

Also not as important but in my prompting I can't figure out how to get the else statement to restart the process if they put a number outside the parameters.

var spec = '!@$%^&*()_+';
var low = 'abcdefghijklmnopqrstuvwxyz';
var num = '0123456789';
var upp = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';

var charLength = prompt("How many characters between 8 - 128?");

if (charLength >= 8, charLength <= 128) {
 var lowChar = confirm("Include lowercase letters?");
 var upChar = confirm("Include uppercase letters?");
 var specChar = confirm("Include special characters?");
 var numChar = confirm("Include numbers?");
}

else {
    var charLength = prompt("How many characters between 8 - 128?");
};

var passwords = document.getElementById("password");
var generate = document.getElementById("btnGen");
var copy = document.getElementById("btnCopy");

generate.addEventListener("click", function(){
    var character = '';
    lowChar ? characters += low : '';
    upChar ? characters += upp : '';
    specChar ? characters += spec : '';
    numChar ? characters += num : '';

    passwords.value = password(charLength.value, characters)
});


function password(l, characters){
    var pwd = '';
    for(var i = 0; i < l; i++){
    pwd += characters.charAt(Math.floor(Math.random() * characters.length))
    }
    return pwd;
}

Thank You!