js实现截图并保存图片（html转canvas、canvas转image）

<h2>原始HTML</h2>
<div style="background:red;width: 600px;" class="test">
    <div style="background:green;">
        <div style="background:blue;">
            <div style="background:yellow;">
                <div style="background:orange;">
                    33333333333333333333333333333333
                </div>
            </div>

        </div>

    </div>
</div>
<h2 class="toCanvas"> <a href="javascript:void(0);"> 转成canvas </a></h2>
<h2 class="toPic"><a href="javascript:void(0);"> 转成图片 </a></h2>
<h5>
    <label for="imgW">宽度:</label>
    <input type="number" value="" id="imgW" placeholder="默认是原图宽度" />
    <label for="imgH">高度:</label>
    <input type="number" value="" id="imgH" placeholder="默认是原图高度" />
    <label for="imgFileName">文件名:</label>
    <input type="text" placeholder="文件名" id="imgFileName" />
    <select id="sel">
                <option value="png">png</option>
                <option value="jpeg">jpeg</option>
                <option value="bmp">bmp</option>
            </select>
    <button id="save">保存</button>
</h5>

<style>
    * {
        margin: 0;
        padding: 0;
    }

    div {
        padding: 20px;
        border: 5px solid black;
    }

    h2 {
        background: #efefef;
        margin: 10px;
    }

    .toPic {
        display: none;
    }
</style>

<script type="text/javascript" src="jquery-3.3.1.js"></script>
<script type="text/javascript" src="html2canvas.min.js"></script>
<script type="text/javascript" src="canvas2image.js"></script>
<script type="text/javascript">
    var test = $(".test").get(0); //将jQuery对象转换为dom对象
    // 点击转成canvas
    $('.toCanvas').click(function(e) {
        // 调用html2canvas插件
        html2canvas(test).then(function(canvas) {
            // canvas宽度
            var canvasWidth = canvas.width;
            // canvas高度
            var canvasHeight = canvas.height;
            // 渲染canvas
            $('.toCanvas').after(canvas);
            // 显示‘转成图片’按钮
            $('.toPic').show(1000);
            // 点击转成图片
            $('.toPic').click(function(e) {
                // 调用Canvas2Image插件
                var img = Canvas2Image.convertToImage(canvas, canvasWidth, canvasHeight);
                // 渲染图片
                $(".toPic").after(img);
                // 点击保存
                $('#save').click(function(e) {
                    let type = $('#sel').val(); //图片类型
                    let w = $('#imgW').val(); //图片宽度
                    let h = $('#imgH').val(); //图片高度
                    let f = $('#imgFileName').val(); //图片文件名
                    w = (w === '') ? canvasWidth : w; //判断输入宽高是否为空，为空时保持原来的值
                    h = (h === '') ? canvasHeight : h;
                    // 调用Canvas2Image插件
                    Canvas2Image.saveAsImage(canvas, w, h, type, f);
                });
            });


        });
    });
</script>