Below is a simple helper function for generating a random alphanumeric string in JavaScript

function randomString(length) {  
    var text = "";
    var possible = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
    for(var i = 0; i < length; i++) {
        text += possible.charAt(Math.floor(Math.random() * possible.length));
    }
    return text;
}