i want to generate a key of pw , why the result is undefined?

why the result is undefined?

let PW = 26;
let pwArray = [0,1,2,3,4,5,6,7,8,9]
let submitEl = document.getElementById("submit");
let element = "";

for (let index = 0; index < pwArray.length; index++) {
    const RandomNum = Math.floor(Math.random()*pwArray.length);
    let pwSlice = pwArray.slice(RandomNum,RandomNum+1);
    let PWc = pwSlice*RandomNum;
     element += pwArray[PWc];

}
console.log(element);

please help,thanks

why the result is undefined?