js 压缩 预览 上传图片

com.js

export const compressImage=function (files,fn,preCallbackFn,i) {
    let newfile = files.files[0];
    let quality = 0.1;
    const name = newfile.name; //文件名
    let reader = new FileReader();
    reader.readAsDataURL(newfile);
    reader.onload = (e) => {
        const src = e.target.result;
        const img = new Image();
        img.src = src;
        img.onload = (e) => {
            const w = img.width;
            const h = img.height;
            //生成canvas
            const canvas = document.createElement('canvas');
            const ctx = canvas.getContext('2d');
            // 创建属性节点
            const anw = document.createAttribute("width");
            anw.nodeValue = w;
            const anh = document.createAttribute("height");
            anh.nodeValue = h;
            canvas.setAttributeNode(anw);
            canvas.setAttributeNode(anh);

            //铺底色 PNG转JPEG时透明区域会变黑色
            ctx.fillStyle = "#fff";
            ctx.fillRect(0, 0, w, h);

            ctx.drawImage(img, 0, 0, w, h);
            // quality值越小，所绘制出的图像越模糊
            const base64 = canvas.toDataURL('image/jpeg', quality); //图片格式jpeg或webp可以选0-1质量区间

            console.log(`原图${(src.length / 1024).toFixed(2)}kb`, `新图${(base64.length / 1024).toFixed(2)}kb`);
            if(base64.length>1024*1024*1){
                return false;
            }

            let arr = base64.split(','), mime = arr[0].match(/:(.*?);/)[1],
                bstr = atob(arr[1]), n = bstr.length, u8arr = new Uint8Array(n);
            while(n--){
                u8arr[n] = bstr.charCodeAt(n);
            }
            let obj = new Blob([u8arr], {type:'image/jpeg'});
            preCallbackFn && preCallbackFn(base64,obj,i);
            fn && fn(obj);
        }
    }
};

//上传图片校验
export const checkImg=function(file){
    var aa=file.value.toLowerCase().split('.');
    if(!(aa[aa.length-1]=='gif'||aa[aa.length-1]=='jpg'||aa[aa.length-1]=='jpeg'||aa[aa.length-1]=='png')){
        throw {code:400,msg:"请选择格式为*.jpg、*.gif、*.jpeg、*.png的图片"};
    }
    var imagSize =  file.files[0].size;
    if(imagSize>1024*1024*1){
        throw {code:401,msg:"图片过大，无法上传"};
    }
    return true;
};

import {checkImg,compressImage} from "com";

 imgPreview(){
          let file=document.getElementById("imgInput");
          try {
              checkImg(file)
          }catch(e) {
              if(e.code==401){
                  if(compressImage(file,this.upImg,this.preCallbackFn) === false){
                      return  alert(e.msg);
                  }
                  return true;
              }else {
                  return  alert(e.msg);
              }
          }
          if (file.files && file.files[0]) {
              let reader = new FileReader();
              reader.onload = function (evt) {
                  let img = document.querySelector('#img_preview img');
                  img.setAttribute('src', evt.target.result);
              }
              reader.readAsDataURL(file.files[0]);
              this.upImg(file.files[0]);
          }
      },

upImg(file){
      let formData = new FormData();
      formData.append("img", file,"image.jpeg");

　　　　//fileUpload 上传为接口

      fileUpload(formData).then(data=>{

          if(!data) return false;
          userModifyImg(data).then(data=>{
              if(!data) return false;
              alert("上传图片成功！")
          });
      });
  },