Nodejs中async/await以及Promise的使用

場景：上傳圖片

注意：try/catch是不能catch住Promise異步異常的

其它：Nest.js中上傳圖片和裁剪

async uploadAction (req, res) {

  try {
   // 同步調用
   await saveFileWithStream(filePath, fileData); // 這里的fileData是Buffer類型
  } catch (err) {
   console.log(err.stack);
  }

}


/**
 * 使用Promise封裝createWriteStream異步事件處理
 * @param {String} filePath [文件路徑]
 * @param {Buffer} readData [Buffer 數據]
 */
static saveFile(filePath, fileData) {

  return new Promise((resolve, reject) => {

  if (!fs.existsSync(filePath)) {
   fs.mkdirSync(filePath);
  }

  // 塊方式寫入文件
  const wstream = fs.createWriteStream(filePath);
 
  wstream.on('open', () => {
   const blockSize = 128;
   const nbBlocks = Math.ceil(fileData.length / (blockSize));
   for (let i = 0; i < nbBlocks; i += 1) {
    const currentBlock = fileData.slice(
     blockSize * i,
     Math.min(blockSize * (i + 1), fileData.length),
    );
    wstream.write(currentBlock);
   }
 
   wstream.end();
  });
  wstream.on('error', (err) => { reject(err); });
  wstream.on('finish', () => { resolve(true); });
 });
}

 

簡化示例版

const requestFunc = async () => {
    let r = null
    try {
      r = await function_async()
    } catch (e) {
      console.error(e.message)
    }
    return r
}
 
return await requestFunc()

 

nodejs文件寫入操作

 
const fs=require('fs');
const path=require('path');
let writeStream=fs.createWriteStream('./test/b.js',{encoding:'utf8'});
 
 
//讀取文件發生錯誤事件
writeStream.on('error', (err) => {
    console.log('發生異常:', err);
});
//已打開要寫入的文件事件
writeStream.on('open', (fd) => {
    console.log('文件已打開:', fd);
});
//文件已經就寫入完成事件
writeStream.on('finish', () => {
    console.log('寫入已完成..');
    console.log('讀取文件內容:', fs.readFileSync('./test/b.js', 'utf8')); //打印寫入的內容
    console.log(writeStream);
});
 
//文件關閉事件
writeStream.on('close', () => {
    console.log('文件已關閉！');
});
 
writeStream.write('這是我要做的測試內容');
writeStream.end();