DOM提供了幾個屬性用來獲取元素大小 - 數字

var box = document.querySelector(".box");
 var w = box.clientWidth;
 var h = box.clientHeight;
 console.log(w,h);

var w1 = box.offsetWidth;
 var h1 = box.offsetHeight;
 console.log(w1,h1);

獲取位置

var small = document.querySelector(".small");
var l = small.offsetLeft;
var t = small.offsetTop;
console.log(l,t);

//或者

做一個直線掉落的div

var box = document.querySelector(".box");
setInterval(function(){
    // 獲取top
    var t = box.offsetTop;
    // 加大
    t += 1
    // 設定給top 
    box.style.top = t + "px"
},
 
10)