Generate unique alphanumeric incrementing string keys

gistfile1.js

#!/usr/bin/env node

var base_str = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ-_";

console.log( number_to_base(process.argv[2], base_str) );

function number_to_base(n, str) {
    if ( n === 0 ) return "0";
    var b = '';
    while ( n > 0 ) {
        b = str[n%str.length] + b;
        n = Math.floor(n / str.length);
    }
    return b;
}