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5画图.html

<!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>Document</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }

        canvas {
            border: 1px solid red;
        }
    </style>
</head>

<body>
    <canvas width="500" height="500"></canvas>
    <script>
        // 获取dom节点
        const canvas = document.querySelector("canvas")
        // 获取画笔
        const ctx = canvas.getContext("2d") // 2d 表示 画的2d图

        canvas.onmousedown = function (event) {
            const mouseX = event.clientX;
            const mouseY = event.clientY;

            ctx.moveTo(mouseX, mouseY);

            canvas.onmousemove = function (e) {
                const mouseX = e.clientX;
                const mouseY = e.clientY;

                ctx.lineTo(mouseX, mouseY);
                ctx.stroke();
            }
        }
        canvas.onmouseup = function () {
            canvas.onmousemove = null;
        }
    </script>
</body>

</html>