<div class="box"></div>

let box = document.querySelector('.box');


let user = {
    'name': prompt('Ваше имя: ', ''),
    'nick': prompt('Ваш ник: ', ''),
    'all': function (welcome, status) {
        box.innerHTML = welcome + ', ' + status + ' ' + this.name + ' ' + this.nick;
    }
}

let userAll = user.all;
userAll('Hi', 'Mr.');