How to Make A Drawing App using HTML5, CSS3 & JavaScript

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In this tutorial, I will teach you how to create a drawing app using HTML5, CSS3, and JavaScript. The complete source code of this JavaScript drawing app is given below.

You can download the full source code (including images) of this JavaScript drawing app at the end of this article.

HTML5, CSS3, and JavaScript Drawing App

index.html

<!DOCTYPE html>
<html lang="en" dir="ltr">
  <head>
    <meta charset="utf-8">
    <title>Drawing App JavaScript</title>
    <link rel="stylesheet" href="style.css">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <script src="script.js" defer></script>
  </head>
  <body>
    <div class="container">
      <section class="tools-board">
        <div class="row">
          <label class="title">Shapes</label>
          <ul class="options">
            <li class="option tool" id="rectangle">
              <img src="icons/rectangle.svg" alt="">
              <span>Rectangle</span>
            </li>
            <li class="option tool" id="circle">
              <img src="icons/circle.svg" alt="">
              <span>Circle</span>
            </li>
            <li class="option tool" id="triangle">
              <img src="icons/triangle.svg" alt="">
              <span>Triangle</span>
            </li>
            <li class="option">
              <input type="checkbox" id="fill-color">
              <label for="fill-color">Fill color</label>
            </li>
          </ul>
        </div>
        <div class="row">
          <label class="title">Options</label>
          <ul class="options">
            <li class="option active tool" id="brush">
              <img src="icons/brush.svg" alt="">
              <span>Brush</span>
            </li>
            <li class="option tool" id="eraser">
              <img src="icons/eraser.svg" alt="">
              <span>Eraser</span>
            </li>
            <li class="option">
              <input type="range" id="size-slider" min="1" max="30" value="5">
            </li>
          </ul>
        </div>
        <div class="row colors">
          <label class="title">Colors</label>
          <ul class="options">
            <li class="option"></li>
            <li class="option selected"></li>
            <li class="option"></li>
            <li class="option"></li>
            <li class="option">
              <input type="color" id="color-picker" value="#4A98F7">
            </li>
          </ul>
        </div>
        <div class="row buttons">
          <button class="clear-canvas">Clear Canvas</button>
          <button class="save-img">Save As Image</button>
        </div>
      </section>
      <section class="drawing-board">
        <canvas></canvas>
      </section>
    </div>
    
  </body>
</html>

script.js

const canvas = document.querySelector("canvas"),
toolBtns = document.querySelectorAll(".tool"),
fillColor = document.querySelector("#fill-color"),
sizeSlider = document.querySelector("#size-slider"),
colorBtns = document.querySelectorAll(".colors .option"),
colorPicker = document.querySelector("#color-picker"),
clearCanvas = document.querySelector(".clear-canvas"),
saveImg = document.querySelector(".save-img"),
ctx = canvas.getContext("2d");

// global variables with default value
let prevMouseX, prevMouseY, snapshot,
isDrawing = false,
selectedTool = "brush",
brushWidth = 5,
selectedColor = "#000";

const setCanvasBackground = () => {
    // setting whole canvas background to white, so the downloaded img background will be white
    ctx.fillStyle = "#fff";
    ctx.fillRect(0, 0, canvas.width, canvas.height);
    ctx.fillStyle = selectedColor; // setting fillstyle back to the selectedColor, it'll be the brush color
}

window.addEventListener("load", () => {
    // setting canvas width/height.. offsetwidth/height returns viewable width/height of an element
    canvas.width = canvas.offsetWidth;
    canvas.height = canvas.offsetHeight;
    setCanvasBackground();
});

const drawRect = (e) => {
    // if fillColor isn't checked draw a rect with border else draw rect with background
    if(!fillColor.checked) {
        // creating circle according to the mouse pointer
        return ctx.strokeRect(e.offsetX, e.offsetY, prevMouseX - e.offsetX, prevMouseY - e.offsetY);
    }
    ctx.fillRect(e.offsetX, e.offsetY, prevMouseX - e.offsetX, prevMouseY - e.offsetY);
}

const drawCircle = (e) => {
    ctx.beginPath(); // creating new path to draw circle
    // getting radius for circle according to the mouse pointer
    let radius = Math.sqrt(Math.pow((prevMouseX - e.offsetX), 2) + Math.pow((prevMouseY - e.offsetY), 2));
    ctx.arc(prevMouseX, prevMouseY, radius, 0, 2 * Math.PI); // creating circle according to the mouse pointer
    fillColor.checked ? ctx.fill() : ctx.stroke(); // if fillColor is checked fill circle else draw border circle
}

const drawTriangle = (e) => {
    ctx.beginPath(); // creating new path to draw circle
    ctx.moveTo(prevMouseX, prevMouseY); // moving triangle to the mouse pointer
    ctx.lineTo(e.offsetX, e.offsetY); // creating first line according to the mouse pointer
    ctx.lineTo(prevMouseX * 2 - e.offsetX, e.offsetY); // creating bottom line of triangle
    ctx.closePath(); // closing path of a triangle so the third line draw automatically
    fillColor.checked ? ctx.fill() : ctx.stroke(); // if fillColor is checked fill triangle else draw border
}

const startDraw = (e) => {
    isDrawing = true;
    prevMouseX = e.offsetX; // passing current mouseX position as prevMouseX value
    prevMouseY = e.offsetY; // passing current mouseY position as prevMouseY value
    ctx.beginPath(); // creating new path to draw
    ctx.lineWidth = brushWidth; // passing brushSize as line width
    ctx.strokeStyle = selectedColor; // passing selectedColor as stroke style
    ctx.fillStyle = selectedColor; // passing selectedColor as fill style
    // copying canvas data & passing as snapshot value.. this avoids dragging the image
    snapshot = ctx.getImageData(0, 0, canvas.width, canvas.height);
}

const drawing = (e) => {
    if(!isDrawing) return; // if isDrawing is false return from here
    ctx.putImageData(snapshot, 0, 0); // adding copied canvas data on to this canvas

    if(selectedTool === "brush" || selectedTool === "eraser") {
        // if selected tool is eraser then set strokeStyle to white 
        // to paint white color on to the existing canvas content else set the stroke color to selected color
        ctx.strokeStyle = selectedTool === "eraser" ? "#fff" : selectedColor;
        ctx.lineTo(e.offsetX, e.offsetY); // creating line according to the mouse pointer
        ctx.stroke(); // drawing/filling line with color
    } else if(selectedTool === "rectangle"){
        drawRect(e);
    } else if(selectedTool === "circle"){
        drawCircle(e);
    } else {
        drawTriangle(e);
    }
}

toolBtns.forEach(btn => {
    btn.addEventListener("click", () => { // adding click event to all tool option
        // removing active class from the previous option and adding on current clicked option
        document.querySelector(".options .active").classList.remove("active");
        btn.classList.add("active");
        selectedTool = btn.id;
    });
});

sizeSlider.addEventListener("change", () => brushWidth = sizeSlider.value); // passing slider value as brushSize

colorBtns.forEach(btn => {
    btn.addEventListener("click", () => { // adding click event to all color button
        // removing selected class from the previous option and adding on current clicked option
        document.querySelector(".options .selected").classList.remove("selected");
        btn.classList.add("selected");
        // passing selected btn background color as selectedColor value
        selectedColor = window.getComputedStyle(btn).getPropertyValue("background-color");
    });
});

colorPicker.addEventListener("change", () => {
    // passing picked color value from color picker to last color btn background
    colorPicker.parentElement.style.background = colorPicker.value;
    colorPicker.parentElement.click();
});

clearCanvas.addEventListener("click", () => {
    ctx.clearRect(0, 0, canvas.width, canvas.height); // clearing whole canvas
    setCanvasBackground();
});

saveImg.addEventListener("click", () => {
    const link = document.createElement("a"); // creating <a> element
    link.download = `${Date.now()}.jpg`; // passing current date as link download value
    link.href = canvas.toDataURL(); // passing canvasData as link href value
    link.click(); // clicking link to download image
});

canvas.addEventListener("mousedown", startDraw);
canvas.addEventListener("mousemove", drawing);
canvas.addEventListener("mouseup", () => isDrawing = false);

style.css

/* Import Google font - Poppins */
@import url('https://fonts.googleapis.com/css2?family=Poppins:[email protected];500;600&display=swap');
*{
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: 'Poppins', sans-serif;
}
body{
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 100vh;
  background: #4A98F7;
}
.container{
  display: flex;
  width: 100%;
  gap: 10px;
  padding: 10px;
  max-width: 1050px;
}
section{
  background: #fff;
  border-radius: 7px;
}
.tools-board{
  width: 210px;
  padding: 15px 22px 0;
}
.tools-board .row{
  margin-bottom: 20px;
}
.row .options{
  list-style: none;
  margin: 10px 0 0 5px;
}
.row .options .option{
  display: flex;
  cursor: pointer;
  align-items: center;
  margin-bottom: 10px;
}
.option:is(:hover, .active) img{
  filter: invert(17%) sepia(90%) saturate(3000%) hue-rotate(900deg) brightness(100%) contrast(100%);
}
.option :where(span, label){
  color: #5A6168;
  cursor: pointer;
  padding-left: 10px;
}
.option:is(:hover, .active) :where(span, label){
  color: #4A98F7;
}
.option #fill-color{
  cursor: pointer;
  height: 14px;
  width: 14px;
}
#fill-color:checked ~ label{
  color: #4A98F7;
}
.option #size-slider{
  width: 100%;
  height: 5px;
  margin-top: 10px;
}
.colors .options{
  display: flex;
  justify-content: space-between;
}
.colors .option{
  height: 20px;
  width: 20px;
  border-radius: 50%;
  margin-top: 3px;
  position: relative;
}
.colors .option:nth-child(1){
  background-color: #fff;
  border: 1px solid #bfbfbf;
}
.colors .option:nth-child(2){
  background-color: #000;
}
.colors .option:nth-child(3){
  background-color: #E02020;
}
.colors .option:nth-child(4){
  background-color: #6DD400;
}
.colors .option:nth-child(5){
  background-color: #4A98F7;
}
.colors .option.selected::before{
  position: absolute;
  content: "";
  top: 50%;
  left: 50%;
  height: 12px;
  width: 12px;
  background: inherit;
  border-radius: inherit;
  border: 2px solid #fff;
  transform: translate(-50%, -50%);
}
.colors .option:first-child.selected::before{
  border-color: #ccc;
}
.option #color-picker{
  opacity: 0;
  cursor: pointer;
}
.buttons button{
  width: 100%;
  color: #fff;
  border: none;
  outline: none;
  padding: 11px 0;
  font-size: 0.9rem;
  margin-bottom: 13px;
  background: none;
  border-radius: 4px;
  cursor: pointer;
}
.buttons .clear-canvas{
  color: #6C757D;
  border: 1px solid #6C757D;
  transition: all 0.3s ease;
}
.clear-canvas:hover{
  color: #fff;
  background: #6C757D;
}
.buttons .save-img{
  background: #4A98F7;
  border: 1px solid #4A98F7;
}
.drawing-board{
  flex: 1;
  overflow: hidden;
}
.drawing-board canvas{
  width: 100%;
  height: 100%;
}

Download Source Code (including images)

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