Layui通过质量比例压缩图片并上传

示例中使用的是Layui 2.5.6版本，需要的请到官网下载

首先添加上传图片的按钮控件：

<button type="button" class="layui-btn" style="margin-top: 10px;width: 100%" id="upload">
    <i class="layui-icon">&#xe67c;</i>上传图片
</button>

然后再JS中初始化Layui并引入upload模块：

<script>
    //一般直接写在一个js文件中
    layui.use(['layer','form','upload'], function(){
        $ = layui.jquery;
        var layer = layui.layer
            ,form = layui.form
            ,upload = layui.upload;
            
        function canvasDataURL(file, callback) { //压缩转化为base64
            var reader = new FileReader()
            reader.readAsDataURL(file)
            reader.onload = function (e) {
                const img = new Image()
                const quality = 0.2 // 图像质量比例
                const canvas = document.createElement('canvas')
                const drawer = canvas.getContext('2d')
                img.src = this.result
                img.onload = function () {
                    canvas.width = img.width
                    canvas.height = img.height
                    drawer.drawImage(img, 0, 0, canvas.width, canvas.height)
                    convertBase64UrlToBlob(canvas.toDataURL(file.type, quality), callback);
                }
            }
        }

        function convertBase64UrlToBlob(urlData, callback) { //将base64转化为文件格式
            const arr = urlData.split(',')
            const mime = arr[0].match(/:(.*?);/)[1]
            const bstr = atob(arr[1])
            let n = bstr.length
            const u8arr = new Uint8Array(n)
            while (n--) {
                u8arr[n] = bstr.charCodeAt(n)
            }
            callback(new Blob([u8arr], {
                type: mime
            }));
        }

        upload.render({
            elem: '#upload' //绑定元素
            ,url: 'XXXXXX' //上传接口
            ,accept : 'images'		//上传文件类型
            ,auto :false  //是否自动上传，这里如果在choose中压缩图片则一定要设置为false否则会无限上传
            ,size : 6144	//上传文件大小限制，单位KB
            ,field : 'img'	//上传文件的字段名
            ,choose: function (obj) { //选择文件后的回调
                var files = obj.pushFile();
                var filesArry = [];
                for (var key in files) { //将上传的文件转为数组形式
                    filesArry.push(files[key])
                }
                var index = filesArry.length - 1;
                var file = filesArry[index]; //获取最后选择的图片,即处理多选情况

                if (navigator.appName == "Microsoft Internet Explorer" && parseInt(navigator.appVersion.split(";")[1]
                    .replace(/[ ]/g, "").replace("MSIE", "")) < 9) {
                    return obj.upload(index, file)
                }
                canvasDataURL(file, function (blob) {
                    var aafile = new File([blob], file.name, {
                        type: file.type
                    })
                    var isLt1M;
                    if (file.size < aafile.size) {
                        isLt1M = file.size
                    } else {
                        isLt1M = aafile.size
                    }

                    if (isLt1M / 1024 / 1024 > 2) {
                        return layer.alert('上传图片过大！')
                    } else {
                        if (file.size < aafile.size) {
                            return obj.upload(index, file)
                        }
                        obj.upload(index, aafile)
                    }
                })
            }
            ,done: function(res){
                if(res.code==0)
                    layer.alert(res.msg, {icon: 6},function (thiswindow) {
                        layer.close(thiswindow);
                    });
                else
                    layer.alert(res.msg, {icon: 5},function (thiswindow) {
                        layer.close(thiswindow);
                    });
            }
            ,error: function(){
                layer.msg("上传失败");
            }
        });

        
    });
</script>