function setup() {

  createCanvas(600, 600);

  angleMode(DEGREES);

}

​

function draw() {

  background(220);

  randomSeed(0);

  var x1 = random(width);

  var y1 = random(height);

  var x2 = random(width);

  var y2 = random(height);

  line(x1, y1, mouseX, mouseY);

  line(x2, y2, mouseX, mouseY);

  push();

  ellipse(x1, y1, 10, 10);

  ellipse(x2, y2, 10, 10);

  pop();

  var b = dist(x1, y1, mouseX, mouseY);

  var c = dist(x2, y2, mouseX, mouseY);

  var a = dist(x1, y1, x2, y2);

  angle = acos((pow(b, 2) + pow(c, 2) - pow(a, 2))/(2 * b * c));

  textSize(20);

  textAlign(CENTER);

  text("Angle: " + round(angle, 1) + "°", width/2, 500);

}