FileReader常见的数据转换

// 文件转 buffer
export async function readBuffer(file) {
  return new Promise((resolve, reject) => {
    const reader = new FileReader();
    reader.onload = loadEvent => resolve(loadEvent.target.result);
    reader.onerror = e => reject(e);
    reader.readAsArrayBuffer(file);
  });
}
// buffer 转 dataUrl
export async function readDataURL(buffer) {
  return new Promise((resolve, reject) => {
    const reader = new FileReader();
    reader.onload = loadEvent => resolve(loadEvent.target.result);
    reader.onerror = e => reject(e);
    reader.readAsDataURL(new Blob([buffer]));
  });
}
// buffer 转 text
export async function readText(buffer) {
  return new Promise((resolve, reject) => {
    const reader = new FileReader();
    reader.onload = loadEvent => resolve(loadEvent.target.result);
    reader.onerror = e => reject(e);
    reader.readAsText(new Blob([buffer]), 'utf-8');
  });
}