Creating a piano in p5.js

I am creating a piano using p5.js. I need help with the color change. When a user presses a key, I want the key to flash a quick color change to let them know that they pressed the key.

In my code, the color does change when you click on the first key, however, when I click a little bit outside the first key, the first key still changes color.

Is my distance a little off? Or is there a more effective way to do this?

function setup() {
  createCanvas(990, 600);
}

function draw() {
  background(220);
  fill(255);
  rect(0, 300, 70, 400);
  rect(70, 300, 70, 400);
  rect(140, 300, 70, 400);
  rect(210, 300, 70, 400);
  rect(280, 300, 70, 400);
  rect(350, 300, 70, 400);
  rect(420, 300, 70, 400);
  rect(490, 300, 70, 400);
  rect(560, 300, 70, 400);
  rect(630, 300, 70, 400);
  rect(700, 300, 70, 400);
  rect(770, 300, 70, 400);
  rect(840, 300, 70, 400);
  rect(910, 300, 70, 400);
  fill(0);
  rect(50, 300, 38, 180);
  rect(120, 300, 38, 180);
  rect(260, 300, 38, 180);
  rect(330, 300, 38, 180);
  rect(400, 300, 38, 180);
  rect(540, 300, 38, 180);
  rect(610, 300, 38, 180);
  rect(750, 300, 38, 180);
  rect(820, 300, 38, 180);
  rect(890, 300, 38, 180);
  text("mouse x: "+mouseX+" mouse y:"+mouseY, width/2,height-30);
 }

function mousePressed() {
  cursor(HAND);

}

function mouseReleased() {
    cursor(ARROW);

let d = dist(mouseX, mouseY, 0, 300);
  if (d < 300) {
    fill(0);
    rect(0, 300, 70, 400);
  }
}

Solution

You're checking whether the mouse position is withing 300 pixels of the point 0,300. This sets up a circle with a center of 0,300 and a radius of 300. Try drawing that in your scene to see where your clickable area is.

Your keys are rectangles, so you should be using point-rectangle intersection to check whether the mouse is inside a particular key. Google is your friend here, but basically you want to check whether mouseX is between the left and right edges, and mouseY is between the top and bottom edges.

Finally, note that you're only ever showing the "flash" for a single frame. I personally can't even see it. You probably want to show the flash for longer, using the millis() function or the frameCount variable for timing. (Again, Google is your friend!)

Shameless self-promotion: here is a tutorial on collision detection, including point-rectangle intersection. It's for Processing, but the ideas are the same in P5.js.