js file上传图片转base64并压缩

/*照片1*/
var scene_pics_map = {};
/*照片2*/
var car_chekc_pics_map = {};
/* 图片预览 */
function imgPreview(obj, type) {
    console.log(1);
    $.showPreloader();
    var file = obj.files[0];

    console.log(obj);
    console.log(file);
    console.log("file.size = " + file.size); // file.size 单位为byte

    var reader = new FileReader();

    // 读取文件过程方法
    reader.onloadstart = function(e) {
        console.log("开始读取....");
    }
    reader.onprogress = function(e) {
        console.log("正在读取中....");
    }
    reader.onabort = function(e) {
        console.log("中断读取....");
    }
    reader.onerror = function(e) {
        console.log("读取异常....");
    }
    reader.onload = function(e) {
        console.log("成功读取....");
        
        var img = document.getElementById("xmTanImg");
        img.src = e.target.result;

        var img_tmp = document.createElement('img');
        // 将文件和文件扩展名拼接
        img.onload = function(){
            /*按比例进行压缩，文件大于1m小于2m的，压缩一半；大于2m小于3m的，压缩为三分之一；以此类推*/
            var scale_ = Math.ceil(file.size/(1024*1024));
            var base64File = cutDowmImg2(img, scale_);
            img_tmp.src = base64File;
            
            // 或者 img.src = this.result; //e.target == this
            var uuid = get_uuid(0, 16);

            $.hidePreloader();
            var html_str = '';
            if(type=='scene'){ 59                 var tmp_ = {
                        'img' : img_tmp.src
                }
                
                scene_pics_map[uuid] = tmp_;
                var scene_pics = JSON.parse($('#scene_pics').val());
                scene_pics.push(img_tmp.src);
                $('#scene_pics').val(JSON.stringify(scene_pics));
                delete tmp_;
            }else if(type=='carcheck') {
                var typeID = $(obj).attr('typeid');
                var tmp_ = {
                        'img' : img_tmp.src,
                        'inspectTypeID' : typeID
                }
                car_chekc_pics_map[uuid] = tmp_;
                var carcheck_detail = JSON.parse($('#carcheck_detail').val());
                carcheck_detail.push({PicPath:img_tmp.src,InspectTypeID:typeID});
                $('#carcheck_detail').val(JSON.stringify(carcheck_detail));
                delete tmp_;
            }else{
                $.alert('falied');
            }
        }
    }

    reader.readAsDataURL(file)
    console.log(scene_pics_map);
    console.log(car_chekc_pics_map);
}
// 压缩图片的方法：按最小宽度压缩
function cutDowmImg(img, width){
    var canvas = document.createElement("canvas");
    $.toast('图片压缩中...'+(img.width)+' :'+width, 2000, 'took');
    canvas.width = Math.min(img.width, width);
    canvas.height = img.height * (width / img.width);
    var cxt = canvas.getContext("2d");
    cxt.drawImage(img, 0, 0, canvas.width, canvas.height);
    return canvas.toDataURL();
}
// 压缩图片的方法：按比例压缩
function cutDowmImg2(img, scal){
    var canvas = document.createElement("canvas");
    $.toast('图片压缩中...1/'+scal, 2000, 'took');
    canvas.width = img.width/scal;
    canvas.height = img.height/scal;
    var cxt = canvas.getContext("2d");
    cxt.drawImage(img, 0, 0, canvas.width, canvas.height);
    return canvas.toDataURL();
}