Promise图片路径转base64

仓储—索赔单—新增页和修改页：

可新增6张图片带压缩点击看大图浏览功能，提交全部转为base64；

修改先把路径赋值到图片框，提交修改时旧图传获取的路径，新图传转换的base64，

在修改中点新增时将旧图路径转为base64再拼接新图的base64，用了promise和async await，因为路径转base64用到image的onload需要做同步处理

vue

async ClaimFormModify_add(){
            var self = this

            //上传图片
            var ary = []
            var aryOld = []
            var img = $('#submit_evaluation_commoditylist').find('.zoomImg').filter(function(index,item) {
                return $(item).attr("src");
            });

            //有await不能用each循环
            for(let i=0;i<img.length;i++){
                let item = img[i]
                var curSrc = $(item).attr('src')
                if(curSrc.indexOf('.') == -1){
                    ary.push(curSrc.split(',')[1])
                }else{
                    var res = await self.dealImage(curSrc)
                    aryOld.push(res)
                    //异步数组为空length为0，但展开有项，有延时问题
                    // self.dealImage(curSrc).then((data)=>{
                    //     aryOld.push(data)
                    // })
                }
            }
            var OldPicsJson = ''
            var imgBase64 = ''
            //异步此时aryOld没有拿到数据，所以拼接也是空的
            ary = aryOld.concat(ary)//旧新图拼接，所有图都当做新图存
            if(ary.length > 0){
                imgBase64 = ary.join(';')
            }

            // console.log(ary,ary.length);

            Ant.showDialog("loding", 1);
            //添加，为当前页面的所有内容提交，页码要累加一次，成功后跳转到第一页
            $.ajax({
                type: 'POST',
                url: "/admin/ClaimForm/ClaimForm_AddDetail",
                data: {
                    StrJson: StrJson
                },
                dataType: "json",
                success: function (msg) {
                    // console.log(msg);
                    if (msg.status.code == "1") {
                        self.curPa = 1
                        self.DetailID = Number(msg.status.sub_msg)
                        if(imgBase64 != ''){
                            //有图片
                            self.uploadImg(imgBase64,OldPicsJson,2)
                        }else{
                            //没图片
                            Ant.showDialog("loding", 0);
                            Ant.alertWindows("提示", "添加成功", 2);
                            self.clearData()
                            self.getDetail()
                        }

                    }
                    else {
                        Ant.alertWindows("提示", msg.status.msg, 2);
                    }
                },
                error: function (a, b, c) {

                }
            });

        },
        //上传图片
        uploadImg:function(imgBase64,OldPicsJson,num){
            var self = this
            $.ajax({
                type: 'POST',
                url: "/admin/ClaimForm/ClaimForm_UpPics",
                data: {
                    ClaimID: self.ClaimID,
                    DetailID: self.DetailID,
                    imgBase64: imgBase64,
                    OldPicsJson: OldPicsJson,
                },
                dataType: "json",
                success: function (msg) {
                    console.log(msg);
                    Ant.showDialog("loding", 0);
                    if (msg.status.code == "1") {
                        if(num == 1){
                            Ant.alertWindows("提示", "修改成功", 2);
                        }else{
                            Ant.alertWindows("提示", "添加成功", 2);
                            self.clearData()
                            self.getDetail()
                        }
                    }
                    else {
                        Ant.alertWindows("提示", msg.status.msg, 2);
                    }
                },
                error: function (a, b, c) {

                }
            });
        },
        dealImage: function(path){
            return new Promise((resolve, reject) => {
                var img = new Image();
                img.src = path;
                img.onload = function () {
                    //默认按比例压缩
                    var w = this.width,//img.
                        h = this.height;//img.
                    var quality = 0.7; // 默认图片质量为0.7

                    //生成canvas
                    var canvas = document.createElement('canvas');
                    var ctx = canvas.getContext('2d');

                    // 创建属性节点
                    // var anw = document.createAttribute('width')
                    // anw.nodeValue = w
                    // var anh = document.createAttribute('height')
                    // anh.nodeValue = h
                    canvas.setAttribute("width", w);//anw
                    canvas.setAttribute("height", h);//anh

                    ctx.drawImage(this, 0, 0, w, h);
                    // quality值越小，所绘制出的图像越模糊
                    var base64 = canvas.toDataURL('image/jpeg', quality);
                    // 回调函数返回base64的值
                    resolve(base64.split(',')[1])
                }
            })
        },    

promise成功后的返回值[[PromiseResult]]中的值如何赋值给变量？

同步
async function app(){
    const f1 = ()=>new Promise(r=>r(1))
    let a = await f1()
    console.log(a)
}
app()

异步
function app(){
    const f1 = ()=>new Promise(r=>r(1))
    f1().then(a=>{
        // 变量a的作用域只能在回调内。在外部声明时，因为线程的争夺当前变量的值是不可靠的
        console.log(a)
    })
}
如果不在用一个函数体内，请参考监听事件EVENT，当监听到old_data不等于new_data时，实现你的回调逻辑

图片路径转base64

// 图片路径
    var img = "imgurl";

    function getBase64Image(img) {
        var canvas = document.createElement("canvas");
        canvas.width = img.width;
        canvas.height = img.height;
        var ctx = canvas.getContext("2d");
        ctx.drawImage(img, 0, 0, img.width, img.height);
        var ext = img.src.substring(img.src.lastIndexOf(".")+1).toLowerCase();
        var dataURL = canvas.toDataURL("image/"+ext);
        return dataURL;
    }
    var image = new Image();
    image.src = img;
    console.log(getBase64Image(image));//一定要把image对象传进去，不能传路径