Transition doesn't work at first time

Question

I have a problem with transition property. Namely, it works only after first time. At the first time there is no transition effect.

JS code:

document.addEventListener("DOMContentLoaded", function() {

  var second = document.querySelector('.square');

  if(second) {
      second.addEventListener("mouseenter", function() {
          var maxX = Math.floor(Math.random() * (window.innerWidth - 200));
          var maxY = Math.floor(Math.random() * (window.innerHeight - 200));
          this.style.left = maxX + 'px';
          this.style.top = maxY + 'px';
          this.style.transition = 'left 2s, top 2s';
      });
  }

 });

CSS code:

* {
margin: 0;
padding: 0;
}

main {
height: 100vh;
display: flex;
justify-content: center;
align-items: center;
position: relative;
}

.second {
height: 200px;
width: 200px;
position: absolute;
display: flex;
justify-content: center;
align-items: center;
}

EDIT:

JSfiddle

UPDATE:

Moving transition to CSS doesn't change anything. Square has to be centered and can't leave the window.

Answer 1

Move transition , top and left to css - browser should know what to transition from and how to transition before you set new X and Y.

 document.addEventListener("DOMContentLoaded", function() { var second = document.querySelector('.square'); if(second) { second.addEventListener("mouseenter", function() { var maxX = Math.floor(Math.random() * (window.innerWidth - 200)); var maxY = Math.floor(Math.random() * (window.innerHeight - 200)); this.style.left = maxX + 'px'; this.style.top = maxY + 'px'; }); } }); 

 .square { background:red; height: 200px; width: 200px; position: absolute; display: flex; justify-content: center; align-items: center; transition: left 2s, top 2s; top: 0; left: 0; } 

 <div class="square"> </div> 

---

EDIT 1

If you want to initially center your square - add this

top: 50%;
left: 50%;
transform: translate(-50%, -50%);

 document.addEventListener("DOMContentLoaded", function() { var second = document.querySelector('.square'); if(second) { second.addEventListener("mouseenter", function() { var maxX = Math.floor(Math.random() * (window.innerWidth - 200)); var maxY = Math.floor(Math.random() * (window.innerHeight - 200)); this.style.left = maxX + 'px'; this.style.top = maxY + 'px'; }); } }); 

 .square { background:red; height: 200px; width: 200px; position: absolute; display: flex; justify-content: center; align-items: center; transition: left 2s, top 2s; top: 50%; left: 50%; transform: translate(-50%, -50%); } 

 <div class="square"> </div> 

---

EDIT 2

Taking into account your fiddle - you should modify your maxX and maxY calculations because transform property moved center of your square from "top left" to "center center":

 document.addEventListener("DOMContentLoaded", function() { var second = document.querySelector('.square'); if(second) { second.addEventListener("mouseenter", function() { var maxX = 100 + Math.floor(Math.random() * (window.innerWidth - 200)); var maxY = 100 + Math.floor(Math.random() * (window.innerHeight - 200)); this.style.left = maxX + 'px'; this.style.top = maxY + 'px'; }); } }); 

 * { margin: 0; padding: 0; } main { height: 100vh; display: flex; justify-content: center; align-items: center; position: relative; } .square { height: 200px; width: 200px; position: absolute; -webkit-box-shadow: 0px 0px 70px 5px rgba(0,0,0,0.5); -moz-box-shadow: 0px 0px 70px 5px rgba(0,0,0,0.5); box-shadow: 0px 0px 70px 5px rgba(0,0,0,0.5); display: flex; justify-content: center; align-items: center; font-size: 20px; transition: left 0.8s, top 0.8s; top: 50%; left: 50%; transform: translate(-50%,-50%); } 

 <main> <div class="square"> <p>catch me!</p> </div> </main>