codice:
<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>test</title>
    <style>
        #canvas {
            width: 300px;
            height: 300px;
            border: 1px solid black;
        }
    </style>
</head>

<body>

    <canvas id="canvas"></canvas>
    <br>
    <label for="photo">Canvas</label>
    <input type="file" name="photo" accept="image/*" id="photo">

    <script>
        const selectPhoto = document.getElementById('photo')
        const canvas = document.getElementById("canvas")

        const cx = canvas.getContext("2d")
        cx.width = 300
        cx.height = 300
        selectPhoto.addEventListener('change', (e) => {
            const img = new Image()
            const url = URL.createObjectURL(e.target.files[0])
            img.src = url

            img.onload = () => {
                let imageWidth = img.width
                let imageHeight = img.height
                let cWidth = cx.width
                let cHeight = cx.height

                let ratio = Math.min((cx.width / img.width), (cx.height / img.height))
                let newWidth = img.width * ratio
                let newHeight = newWidth / 2
                cx.clearRect(0, 0, cx.width, cx.height)
                cx.drawImage(img, 0, 0, img.width, img.height, 0, 0, newWidth, newHeight)
                URL.revokeObjectURL(url)
            }
        })

    </script>
</body>

</html>