app.js

// your code goes here.
var element = document.querySelector('.block');
var ball = document.querySelectorAll('.ball');

var count = 0;

function fn (e) {
    var coords = {
        x: 0,
        y: 0
    };
    coords.x = e.x;
    coords.y = e.y;
    for (var i = 0; i < ball.length; ++i) {
        ball[i].style.top = coords.y + 'px';
        ball[i].style.left = coords.x + 'px';
    }
}

element.addEventListener('click', fn, false);