Generate random String with a specific sign in it using JS

Is there a way to generate random String using JS. With '@', '.' sign in it I have been search for random string generation between a specific range this code works

function stringGen(len) {
    var text = " ";
    var charset = "abcdefghijklmnopqrstuvwxyz0123456789";

    for( var i=0; i < len; i++ ) {
        text += charset.charAt(Math.floor(Math.random() * charset.length));
    }

    return text;
}

console.log(stringGen(3));

but there is no specific sign it it. I am creating a random email generator so please help me guys!