//页面显示转换后的图片
            <img
              v-for="(item, i) in imageBase64"
            :key="i"
            :src="item.url"
              />

imageBase64: [], // 附件预览

 根据后端返回的base64 我这没有返回前缀 所以手动加上

import { pdf_img } from '@/components/test/FileTypeConversion.js';
querytest(tab) {
      // 预览附件
        this.imageBase64 = [];
        querytest(obj)
          .then((res) => {
            if (res.data.code == '0') {
              const arr = res.data.data;
                  const a = pdf_img(
                    'data:application/pdf;base64,' + arr[i].imageBase64,
                    'pdf',
                    'base64',
                  );
                  a.Callback = (obg) => {
                    for (let i = 0; i < obg.length; i++) {
                      let obj = {};
                      obj.url = obg[i];
                      this.imageBase64.push(obj);
                    }
                  };              
            } 
          })
    },

 封装好的工具类 FileTypeConversion.js

import pdf from "vue-pdf";
import JsPDF from 'jspdf';
import { changeUrl } from "./appendix.js";
export function pdf_canvas(file,type,fileForm){
  // pdf转canvas
  const onloadFile = {};
  const canvasArr = [];
  let numPages = 0;
  changeUrl(file,type,fileForm + '_url').then(perfix64 => {
    const CMAP_URL = "https://unpkg.com/pdfjs-dist@2.0.943/cmaps/";
    const src = pdf.createLoadingTask({
      url: perfix64,
      withCredentials: false,
      cMapUrl: CMAP_URL,
      cMapPacked: true
    });
    src.promise.then(pdf => {
      for(let i = 1,l = pdf.numPages; i <= l; i++) {
        numPages = pdf.numPages;
        pdf.getPage(i).then((page) => {
          const canvas = document.createElement("canvas");
          const ctx = canvas.getContext('2d');
          const viewport = page.getViewport({ scale: 1.5 });
          canvas.height = viewport.height;
          canvas.width = viewport.width;
          canvas.style.width = viewport.width + 'px';
          canvas.style.height = viewport.height + 'px';
          page.render({
            canvasContext: ctx,
            viewport,
          });
          canvasArr.push(canvas);
          if(numPages == i){
            onloadFile.Callback ? onloadFile.Callback(canvasArr) : '';
          }
        });
      }
    })
    .catch(err => {
      console.error("pdf 加载失败", err);
    });
  });
  return onloadFile
}
export function canvas_img(canvas){
  // canvas转img
  return canvas.toDataURL("image/png");
}
export function pdf_img(file,type,fileForm){
  // pdf转img
  const onloadFile = {};
  const imgList = [];
  const canvas = pdf_canvas(file,type,fileForm);
  canvas.Callback = function(canvasArr){
    setTimeout(() => {
      for(let i = 0 ;i < canvasArr.length;i++){
        imgList.push(canvasArr[i].toDataURL("image/png"));
      }
      onloadFile.Callback ? onloadFile.Callback(imgList) : '';
    },(1000+150*canvasArr.length));
  }
  return onloadFile;
}

export function img_canvas(file,fileForm){
  // img转canvas
  const onloadFile = {};
  changeUrl(file,fileForm,fileForm + '_url').then(url => {
    const img = new Image();  //创建一个临时存储
    img.src = url //将图片数据赋值即可
    img.onload = function(){  //定义加载图片后弹出显示
      const canvas = document.createElement("canvas");
      canvas.width = img.width;
      canvas.height = img.height;
      this.ctx = canvas.getContext("2d");
      this.ctx.drawImage(img,0,0,img.width,img.height);
      onloadFile.Callback ? onloadFile.Callback(canvas) : '';
      img.remove();
    };
  })
  return onloadFile;
}

export function img_pdf(file,fileForm){
  // img转pdf
  const onloadFile = {};
  const canvas = img_canvas(file,fileForm);
  canvas.Callback = function(canvas){
    const base64pdf = canvas_pdf(canvas);
    onloadFile.Callback ? onloadFile.Callback(base64pdf) : '';
  }
  return onloadFile;
}

export function canvas_pdf(canvas){
  // canvas转pdf
  const canvasUrl = canvas.toDataURL('image/jpeg');
  const pdf = new JsPDF('x', 'px', [canvas.width, canvas.height]);
  pdf.addImage(canvasUrl, 'PNG', 0, 0, canvas.width, canvas.height);
  let base64pdf = pdf.output('datauristring');
  base64pdf = base64pdf.replace('data:application/pdf;filename=generated.pdf;base64,', 'data:application/pdf;base64,');
  return base64pdf;
}

changURl-->appendix.js

const fileType = {
    "pdf":{
        type:"application/pdf;charset=utf-8",// 文件转换类型
        base64Type:"data:application/pdf;base64,",// base64前缀
    },
    "img":{
        // img适用所有通用图片格式
        type:"image/png",
        base64Type:"data:image/png;base64,",
    },
    "gif":{
        type:"image/gif",
        base64Type:"data:image/gif;base64,",
    },
    "doc":{
        type:"application/msword",
        base64Type:"data:application/msword;base64,"
    },
    "docx":{
        type:"application/vnd.openxmlformats-officedocument.wordprocessingml.document",
        base64Type:"data:application/vnd.openxmlformats-officedocument.wordprocessingml.document;base64,"
    },
    "xls":{
        type:"application/vnd.ms-excel",
        base64Type:"data:application/vnd.ms-excel;base64,"
    },
    "xlsx":{
        type:"application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
        base64Type:"data:application/vnd.openxmlformats-officedocument.spreadsheetml.sheet;base64,"
    },
    "ppt":{
        type:"application/vnd.ms-powerpoint",
        base64Type:"data:application/vnd.ms-powerpoint;base64,"
    },
    "pptx":{
        type:"application/vnd.openxmlformats-officedocument.presentationml.presentation",
        base64Type:"data:application/vnd.openxmlformats-officedocument.presentationml.presentation;base64,"
    },
    "txt":{
        type:"text/plain",
        base64Type:"data:text/plain;base64,"
    },
}
let files,types,changeTypes;

// file 附件
// type 文件类型(img,pdf)
// changeType 附件转换类型(base64 blob url),三者互转(列如:base64_url)
export async function changeUrl(file,type,changeType) { 
    if(!file || !type || !changeType || !fileFun[changeType]) {
        return file;
    };
    files = file;
    types = type;
    changeTypes = changeType;
    const fileWj = await fileFun[changeType](file);
    return fileWj;
}
function base64_url(file){
    // base64转url
    const blob = base64_blob(file);
    return window.URL.createObjectURL(blob);
}
function base64_blob(file){
    // base64转blob
    const arr = file.split(",")
    const mime = arr[0].match(/:(.*?);/)[1];
    const bstr = atob(arr[1]);
    let n = bstr.length;
    const u8arr = new Uint8Array(n);
    while (n--) {
        u8arr[n] = bstr.charCodeAt(n)
    }
    return new Blob([u8arr], { type: mime });
}
function blob_url(file){
     // blob转url
    const blob = new Blob([file], {type: fileType[types].type});
    return URL.createObjectURL(blob);
}
function blob_base64(file){
    // blob转base64
    return new Promise((resolve) => {
        const reader = new FileReader();
        reader.readAsDataURL(file);
        reader.onload = () => {
            const arr = reader.result.split(",");
            resolve(fileType[types].base64Type + arr[1]);
        };
    });
}
async function url_blob(url) {
    // url转blob
    return new Promise((resolve) => {
        const xhr = new XMLHttpRequest();
        xhr.open('GET',url,true);
        xhr.responseType = 'blob';
        xhr.onload = function(e) {
            const myBlob = this.response;
            // let files = new window.File([myBlob], myBlob.type, {type:myBlob.type}) // myBlob.type 自定义文件名
            resolve(myBlob)
        };
        xhr.send();
    })
}
async function url_base64(url){
    // url转base64
    const blob = await url_blob(url);
    return new Promise((resolve) => {
        blob_base64(blob).then(res => {
            resolve(res)
        });
    })
}

const fileFun = {
    "base64_url":base64_url,
    "blob_url":blob_url,
    "base64_blob":base64_blob,
    "blob_base64":blob_base64,
    "url_blob":url_blob,
    "url_base64":url_base64,
}

最后预览效果