promise问题
 发布于 9 年前  作者 postgetme  4458 次预览  最后一次回复是 9 年前  来自 问答 

怎么我的代码先打印‘download over’,后执行下载呢???

function downloadAsync(url, name) {
  return new Promise(function(resolve, reject) {
    request(url, function(err, response, body) {
      if (err) {
        reject(err);
      } else {
        fs.writeFileSync(path.resolve(process.cwd(), 'downloaded_html', name), body);
        console.log('got ' + url);
        resolve();
      }
    })
  })
}

var urls = ['url1', 'url2', 'url3']

var promises = urls.map(function(url, i) {
  var name = i + '.html'
  downloadAsync(url, name)
})

Promise.all(promises).then(function() {
  console.log('download over')
})
4 回复
postgetme
var promises = urls.map(function(url, i) {
  var name = i + '.html'
  return  downloadAsync(url, name)
})

加个return就好了

klesh

用箭头函数,可以省略 return

var promises = urls.map((url, i) => downloadAsync(url, i + '.html'))
magicdawn

Array.prototype.map 的并发是 Infinity, 要控制并发可以使用