字符串转base-64 。

btoa()

base64转字符串

atob()

base64转blob

function dataUrlToFile(dataurl, filename) {
  let arr = dataurl.split(","),
  mime = arr[0].match(/:(.*?);/)[1],
  bstr = atob(arr[1]),
  n = bstr.length,
  u8arr = new Uint8Array(n);
  while (n--) {
    u8arr[n] = bstr.charCodeAt(n);
  }
  return new File([u8arr], filename, { type: mime });
}
// 使用示例
let file = dataUrlToFile('data:text/plain;base64,aGVsbG8gd29ybGQ=','hello.txt');
console.log(file);

base64转File对象

function dataUrlToFile(dataurl, filename) {
  let arr = dataurl.split(","),
  mime = arr[0].match(/:(.*?);/)[1],
  bstr = atob(arr[1]),
  n = bstr.length,
  u8arr = new Uint8Array(n);
  while (n--) {
    u8arr[n] = bstr.charCodeAt(n);
  }
  return new File([u8arr], filename, { type: mime });
}

// 使用示例
let file = dataUrlToFile('data:text/plain;base64,aGVsbG8gd29ybGQ=','hello.txt');
console.log(file);

URL 转 File 对象

function urlToFile(url, filename, mimeType) {
  return fetch(url).then((res) => {
    return res.arrayBuffer();
  }).then((buffer) =>{
    return new File([buffer], filename, { type: mimeType });
  });
}

// 使用示例
urlToFile('data:text/plain;base64,aGVsbG8gd29ybGQ=', 'hello.txt','text/plain')
  .then(function(file){ console.log(file);});