const chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
const maxLength = 10;

const indeces = [0];

while (indeces.length < maxLength) {

    let string = ""
    for (let i = 0; i < indeces.length; i++) {
        string += chars[indeces[i]]
    }
    console.log(string);

    let lastElementIndex = indeces.length - 1;

    increase(lastElementIndex);

    function increase (index) {

        //Room to increase
        if (indeces[index] < chars.length - 1)
            indeces[index]++;

        //No room to increase, increase element before last
        else {

            //overflow it
            indeces[index] = 0;

            //Already at start, add new character
            if (index == 0)
                indeces.unshift(0);

            //Otherwise increase character before index
            else increase(index-1)
        }

    }

}