1. 代碼片段

const http = require('http');
const fs = require('fs');
const path = require('path');

const dest = path.join('custom_path', 'filename.extname');
// 你可能需要自行確保該路徑存在
const file = fs.createWriteStream(dest);

http.get(uri, (res)=>{
  if(res.statusCode !== 200){
    cb(response.statusCode);
    return;
  }

  res.on('end', ()=>{
    console.log('finish download');
  });

  // 進度、超時等

  file.on('finish', ()=>{
    file.close();
  }).on('error', (err)=>{
    fs.unlink(dest);
  });

  res.pipe(file);
});

2. 封裝callback

const http = require('http');
const fs = require('fs');

function downloadFile(uri, dest, cb){
  // 確保dest路徑存在
  const file = fs.createWriteStream(dest);

  http.get(uri, (res)=>{
    if(res.statusCode !== 200){
      cb(response.statusCode);
      return;
    }

    res.on('end', ()=>{
      console.log('download end');
    });

    // 進度、超時等

    file.on('finish', ()=>{
      console.log('finish write file')
      file.close(cb);
    }).on('error', (err)=>{
      fs.unlink(dest);
      if(cb) cb(err.message);
    })

    res.pipe(file);
  });
}

3. Promise化，支持async, await調(diào)用

const http = require('http');
const fs = require('fs');

function downloadFileAsync(uri, dest){
  return new Promise((resolve, reject)=>{
      // 確保dest路徑存在
    const file = fs.createWriteStream(dest);

    http.get(uri, (res)=>{
      if(res.statusCode !== 200){
        reject(response.statusCode);
        return;
      }

      res.on('end', ()=>{
        console.log('download end');
      });

      // 進度、超時等

      file.on('finish', ()=>{
        console.log('finish write file')
        file.close(resolve);
      }).on('error', (err)=>{
        fs.unlink(dest);
        reject(err.message);
      })

      res.pipe(file);
    });
  });
}

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