小时候都玩过数字连线画册，这里我们用canvas将它实现

逻辑要点：

canvas无法进行回撤操作，即每一步都需要完整的重新绘制
为了体验更好此处做了一个简单的矩形范围吸附效果，完善可以更改成圆形范围

演示链接：

点我

源码如下：

<!DOCTYPE html>
<html>

<head>
    <meta charset="utf-8">
    <title>小互动-数字连线</title>
    <meta name="viewport"
        content="user-scalable=no, width=device-width, initial-scale=1, maximum-scale=1,viewport-fit=cover">
</head>
<style>
    body {
        background-color: gray;
    }

    #canvas {
        position: absolute;
        background-image: url(./numconnect.jpeg);
    }
</style>


<body style="margin:0;padding:0;" ontouchmove="javascript:window.event.preventDefault();">
    <canvas id="canvas" width="300" height="426"></canvas>
</body>
<script type="text/javascript">
    let points = [
        101, 340,
        58, 356,
        16, 292,
        61, 10,
        46, 294,
        106, 179,
        196, 140,
        224, 120,
        275, 146,
        287, 184
    ]

    let cv = document.getElementById('canvas');
    let ctx = cv.getContext("2d");
    let connectOver = false;
    let curIndex = 0;
    let limit = 10;
    draw();

    function draw() {
        ctx.clearRect(0, 0, cv.width, cv.height);
        for (let index = 0; index < points.length; index += 2) {
            const x = points[index];
            const y = points[index + 1];
            if (index > 0 && index <= 2 * curIndex) {
                drawLine(ctx, points[index - 2], points[index - 1], x, y)
            }
            drawPoint(ctx, x, y);
        }
    }

    function drawLine(ctx, sx, sy, ex, ey) {
        ctx.beginPath()
        ctx.moveTo(sx, sy)
        ctx.lineTo(ex, ey);
        ctx.lineWidth = 4;
        ctx.strokeStyle = '#000';
        ctx.stroke();
    }

    function drawPoint(ctx, cx, cy) {
        let R = 4
        ctx.save();
        ctx.fillStyle = '#000';
        ctx.beginPath();
        ctx.arc(cx, cy, R, 0, Math.PI * 2);
        ctx.fill();
        ctx.restore();
    }

    document.addEventListener('mousedown', onDocumentMouseDown, false);

    function onDocumentMouseDown(event) {
        event.preventDefault();
        document.addEventListener('mousemove', onDocumentMouseMove, false);
        document.addEventListener('mouseup', onDocumentMouseUp, false);
    }

    function onDocumentMouseMove(event) {
        var x = event.clientX;
        var y = event.clientY;
        moveEvent(x, y);
    }

    function onDocumentMouseUp() {
        upEvent();
        document.removeEventListener('mousemove', onDocumentMouseMove);
        document.removeEventListener('mouseup', onDocumentMouseUp);
    }

    document.addEventListener('touchstart', onDocumentTouchStart, false);
    document.addEventListener('touchmove', onDocumentTouchMove, false);
    document.addEventListener('touchend', onDocumentTouchEnd, false);

    function onDocumentTouchStart() {

    }

    function onDocumentTouchMove(event) {
        let x = event.changedTouches[0].clientX;
        let y = event.changedTouches[0].clientY;
        moveEvent(x, y);
    }

    function onDocumentTouchEnd(event) {
        upEvent();
    }

    function moveEvent(x, y) {
        if (connectOver) {
            return;
        }
        draw();
        drawLine(ctx, points[2 * curIndex], points[2 * curIndex + 1], x, y);

        let tx = points[2 * (curIndex + 1)];
        let ty = points[2 * (curIndex + 1) + 1];
        if (Math.abs(x - tx) < limit && Math.abs(y - ty) < limit) {
            curIndex += 1;
            draw();
        }
        if (curIndex == points.length / 2 - 1) {
            connectOver = true;
            alert("连完了")
        }
    }

    function upEvent() {
        if (connectOver) {
            return;
        }
        draw();
    }
</script>
</html>