check if the mouse is inside

sketch.js

function Thing (_x,_y,_diam){
  this.x = _x;
  this.y = _y;
  this.diam = _diam;
  this.over = false;

this.display = function(){


  if(this.over === true){
      fill(128);
    }else{
      fill(0);
    }


    ellipse(this.x,this.y,this.diam,this.diam);
  }


this.isInside = function(){
      var d = dist(mouseX,mouseY,this.x,this.y);
    if(d > this.diam/2){
      this.over = true;
    }else{
      this.over = false;
    }
}
 // this.update = function (){
 //  this.x = this.x + random(-1,1);
 //  this.y = this.y + random(-1,1);
 //  this.diam = this.diam + random(-1,1);
 // }
}

var hansolo = null;
var things = [];
function setup(){
  var canvas = createCanvas(500,500);
  canvas.parent('sketch');
  var x = width/2;
  var y = height/2;
  var diam = 20;

  things.push(new Thing(x,y, diam));
  things.push(new Thing(x,100, diam));
  things.push(new Thing(20,y, diam));

   hansolo = new Thing(10,10,30);
}

function draw(){
  background(255);

  hansolo.isInside();
  hansolo.display();


  for(var i = 0; i < things.length;i++){
    things[i].isInside();
    things[i].display();
    // things[i].update();

  }

}

index.html

<!doctype html>
<html lang="en">
  <head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
    <title>{page.title}</title>
    <meta name="description" content="something">
    <meta name="author" content="me">
  </head>
  <body>
    <script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/p5.js/0.4.17/p5.min.js"></script>
    <script type="text/javascript" src="sketch.js"></script>
    <div id="sketch"></div>
  </p>

</body>
</html>