1、图片file对象转base64

//将图片文件对象转成base64值
//例如：使用上传图片antd-Upload组件时，就可能用到
import React, { useState } from 'react';
import { Upload, Button } from 'antd';

export default function Img() {
  const [base64, setBase64] = useState('');
  const imgFileToBase64 = (file: File) => {
    return new Promise((resolve, reject) => {
      const reader = new FileReader();
      reader.readAsDataURL(file);
      reader.onload = () => resolve(reader.result);
      reader.onerror = (error) => reject(error);
    });
  };
  //上传图片，将上传到图片base64放到其他img中展示
  return (
    <div>
      <Upload
        name="file"
        customRequest={async (info: any) => {
          const base64ImgWhole: any = await imgFileToBase64(info.file);
          //如果需要将图片base64给后台，则需要将data.*base64去掉
          const base64Img = base64ImgWhole.replace(/^data.*base64,/, '');
          setBase64(base64ImgWhole);
        }}
        showUploadList={false}
      >
        <Button>上传图片</Button>
      </Upload>
      {base64 && <img src={base64} />}
    </div>
  );
}

2、将图片的url转为base64

//通过canvas.toDataURL()将图片转成base64值
const getImgBase64 = (url: any, callback: any) => {
  //创建image对象
  let img = new Image();
  img.src = url;
  //setAttribute()设置元素属性
  //设置图片允许跨域，否则canvas转base64时，toDataURL会报错
  img.setAttribute('crossOrigin', 'anonymous');
  img.onload = () => {
    //创建canvas元素
    const canvas = document.createElement('canvas');
    //使用naturalWidth，naturalHeight使图片更准确
    canvas.width = img.naturalWidth;
    canvas.height = img.naturalHeight;
    const ctx = canvas.getContext('2d');
    ctx?.drawImage(img, 0, 0);
    const base64 = canvas.toDataURL('image/png');
    //回调函数 将data:image/png;base64,去掉后，可传给后台
    callback(base64.replace("data:image/png;base64,", ""));
  };
}