web移动端对上传头像图片进行压缩，当图片过大的时候压缩不成功但是也没有报错

Question

这两天在做移动端上传头像功能，想对大于400kb的图片进行压缩再上传，压缩大于400kb的图片一直没成功，也没有报什么错误，后来我重新看了自己的代码，发现是因为当图片大小大于400kb的时候，压缩图片函数传入的base64Img参数我写错了，真的是太粗心，现在将正确的代码附上：

uploadImg() {
      let vm = this;
      console.log(vm.temp);
      var img = document.getElementById("phoneImage"),
        maxSize = 400 * 1024; //400kb
      var imgFile = new FileReader();
      imgFile.readAsDataURL(img.files[0]);
      imgFile.onload = function() {
        vm.temp.base64Img = imgFile.result;
        if (vm.temp.base64Img.length < maxSize) {
          //图片直接上传
          alert("<=100kb;size=" + vm.temp.base64Img.length);
          uploadImage(vm.temp).then(response => {
            const data = response.data;
            vm.temp = data.data;
            setTimeout(() => {
              vm.$router.push({
                path: "/setting"
              });
              window.location.reload();
            }, 5);
          });
        } else {
          //  >400kb,压缩再上传
          
          vm.compress(vm.temp.base64Img, function(base64Img) {
            uploadImage({ base64Img }).then(response => {
              const data = response.data;
              setTimeout(() => {
                vm.$router.push({
                  path: "/setting"
                });
                window.location.reload();
              }, 5);
            });
          });
        }
      };
    },
    compress(base64Img, callback) {
      var img = new Image();
      img.src = base64Img;
      img.onload = function() {
        var width = img.width;
        var height = img.height;
        var canvas = document.createElement("canvas");
        canvas.width = width;
        canvas.height = height;
        canvas.getContext("2d").drawImage(img, 0, 0, width, height);
        callback(canvas.toDataURL("image/jpeg", 0.05));
      };
    }

Answer 1

你这个压缩图片有问题
你this.compress(vm.temp.base64Img);传入的是base64格式的字符串
canvas.width = img.width; canvas.height = img.height;这里base64格式的字符串是获取不到宽高的
这句canvas.toDataURL("image/jpeg", 0.15)你之前没有把图片画到canvas上所以的canvas上是空的

callback：

compress(base64img,callback) {
    var img = new Image();
    img.src = base64img;
    img.onload = function(){
        var width = img.width;
        var height = img.height;
        var canvas = document.createElement("canvas");
        canvas.width = width;
        canvas.height = height;
        canvas.getContext("2d").drawImage(img,0,0,width,height);
        callback(canvas.toDataURL("image/jpeg", 0.15))
    }
}
//调用
vm.compress(vm.temp.base64img, function (base64img) {
    uploadImage({ base64img }).then(response => {
        const data = response.data;
        //...
    });
});

promise：

function compress(base64img, callback) {
    return new Promise(function (resolve) {
        var img = new Image();
        img.src = base64img;
        img.onload = function () {
            var width = img.width;
            var height = img.height;
            var canvas = document.createElement("canvas");
            canvas.width = width;
            canvas.height = height;
            canvas.getContext("2d").drawImage(img, 0, 0, width, height);
            resolve(canvas.toDataURL("image/jpeg", 0.15))
        }
    })
}
//调用
vm.compress(vm.temp.base64img)
    .then(base64img => uploadImage({ base64img }))
    .then(response => {
        const data = response.data;
        //...
    });

Answer 2

很感谢李十三大神的帮忙，现在附上正确的代码

uploadImg() {
      let vm = this;
      console.log(vm.temp);
      var img = document.getElementById("phoneImage"),
        maxSize = 400 * 1024; //400kb
      var imgFile = new FileReader();
      imgFile.readAsDataURL(img.files[0]);
      imgFile.onload = function() {
        vm.temp.base64Img = imgFile.result;
        if (vm.temp.base64Img.length < maxSize) {
          //图片直接上传
          alert("<=100kb;size=" + vm.temp.base64Img.length);
          uploadImage(vm.temp).then(response => {
            const data = response.data;
            vm.temp = data.data;
            setTimeout(() => {
              vm.$router.push({
                path: "/setting"
              });
              window.location.reload();
            }, 5);
          });
        } else {
          //  >400kb,压缩再上传
          
          vm.compress(vm.temp.base64Img, function(base64Img) {
            uploadImage({ base64Img }).then(response => {
              const data = response.data;
              setTimeout(() => {
                vm.$router.push({
                  path: "/setting"
                });
                window.location.reload();
              }, 5);
            });
          });
        }
      };
    },
    compress(base64Img, callback) {
      var img = new Image();
      img.src = base64Img;
      img.onload = function() {
        var width = img.width;
        var height = img.height;
        var canvas = document.createElement("canvas");
        canvas.width = width;
        canvas.height = height;
        canvas.getContext("2d").drawImage(img, 0, 0, width, height);
        callback(canvas.toDataURL("image/jpeg", 0.05));
      };
    }