Create a basic drawing web app with JavaScript - Part 1

Create a basic drawing application - that draws circles, using a canvas element with a click handler. The handler will monitor clicks on the canvas, triggering a function to draw a circle at the clicked position. Additionally, include input boxes for users to adjust the R, G, and B components of the color, these will need to range from 0 to 255, a slider to adjust the radius of the circle drawn and finally a button to clear the canvas.

Solution

let canvas = document.querySelector("#canvas");
let ctx = canvas.getContext("2d");

let redColor = 0;
let greenColor = 0;
let blueColor = 0;

let opacity = 1;
let radius = 100;

let width = canvas.width;
let height = canvas.height;

// handle red value
document.querySelector("#redColor").addEventListener("change", (event) => {
  let newRedValue = event.target.value;
  if (newRedValue >= 0 && newRedValue <= 255) {
    redColor = newRedValue;
    return;
  }

  redColor = 0;
});

// handle green value
document.querySelector("#greenColor").addEventListener("change", (event) => {
  let newGreenValue = event.target.value;
  if (newGreenValue >= 0 && newGreenValue <= 255) {
    greenColor = newGreenValue;
    return;
  }

  greenColor = 0;
});

// handle blue value
document.querySelector("#blueColor").addEventListener("change", (event) => {
  let newBlueValue = event.target.value;
  if (newBlueValue >= 0 && newBlueValue <= 255) {
    blueColor = newBlueValue;
    return;
  }

  blueColor = 0;
});

// handle opacity
document.querySelector("#transparent").addEventListener("change", (event) => {
  let newValue = event.target.value;
  if (newValue >= 0 && newValue <= 100) {
    opacity = (newValue * 1.0) / 100;
    return;
  }

  opacity = 1;
});

// handle radius
document.querySelector("#radius").addEventListener("change", (event) => {
  let newRadiusValue = event.target.value;
  radius = newRadiusValue * 100;
});

function createCircle(x, y) {
  ctx.fillStyle = `rgba(${redColor}, ${greenColor}, ${blueColor}, ${opacity})`;
  ctx.beginPath();
  ctx.arc(x, y, radius, 0, Math.PI * 2, false);
  ctx.fill();
}

canvas.addEventListener("click", (event) => {
  createCircle(event.offsetX, event.offsetY);
});

document.querySelector("#clear").addEventListener("click", () => {
  ctx.clearRect(0, 0, width, height);
});

Result

Continuation
Checkout Part 2