function startUpload(fileId,site){    var this_=$(fileId);    var front;    if(site=='back' || site=='head'){        front=$('#front').val();        if(front.length==0){            layer.msg('请先上传身份证正面照');            return;        }    }    readAsDataURL( fileId,function(img){        this_.prev().attr({src : img});        this_.show();        this_.next().val(img);        });}/** * 读取图片为base64数据 返回 base64图片 * @param file 文件 * @param callback 回调函数 */function readAsDataURL(fileId,callback){    var file = $(fileId).get(0).files[0];    var reader = new FileReader();    var image = new Image();    var canvas = createCanvas();    var ctx = canvas.getContext("2d");    reader.onload = function(){ // 文件加载完处理        var result = this.result;        image.onload = function(){ // 图片加载完处理            var imgScale = imgScaleW(800,this.width,this.height);            canvas.width = imgScale.width;            canvas.height = imgScale.height;            ctx.drawImage(image,0,0,imgScale.width,imgScale.height);            var dataURL = canvas.toDataURL('image/jpeg'); // 图片base64            ctx.clearRect(0,0,imgScale.width,imgScale.height); // 清除画布            callback (dataURL); //dataURL:处理成功返回的图片base64        };        image.src = result;    };    reader.readAsDataURL(file);}/** *  创建画布 * @returns */function createCanvas(){    var canvas = document.getElementById('canvas');    if(!canvas){        var canvasTag = document.createElement('canvas');        canvasTag.setAttribute('id','canvas');        canvasTag.setAttribute('style','display:none;');//隐藏画布        document.body.appendChild(canvasTag);        canvas = document.getElementById('canvas');    }    return canvas;}/** * 图片压缩 * @param maxWidth 最大宽度或最大高度 * @param width 宽度 * @param height 高度 * @returns {___anonymous1968_1969} */function imgScaleW(maxWidth,width,height){    var imgScale = {};    var w = 0;    var h = 0;    if(width <= maxWidth && height <= maxWidth){ // 如果图片宽高都小于限制的最大值,不用缩放        imgScale = {                width:width,                height:height        };    }else{        if(width >= height){ // 如果图片宽大于高            w = maxWidth;            h = Math.ceil(maxWidth * height / width);        }else{     // 如果图片高大于宽            h = maxWidth;            w = Math.ceil(maxWidth * width / height);        }        imgScale = {                width:w,                height:h        };    }    return imgScale;}