用NODE.JS中的流编写工具是要注意的事项

'use strict';
const fs = require('fs');
const co = require('co');

function getSomeDataFromStream (stream) {
 let data = stream.read();
 if (data) return Promise.resolve(data);

 if (!stream.readable) return Promise.resolve(null);

 return new Promise((resolve, reject) => {
  stream.once('readable', () => resolve(stream.read()));
  stream.on('error', reject);
  stream.on('end', resolve);
 })
}

let stream = fs.createReadStream('/Path/to/a/big/file');

co(function *() {
 let chunk;
 while ((chunk = yield getSomeDataFromStream(stream)) !== null) {
  console.log(chunk);
 }
}).catch(console.error);

function getSomeDataFromStream (stream) {
 let data = stream.read();
 if (data) return Promise.resolve(data);

 if (!stream.readable) return Promise.resolve(null);

 return new Promise((resolve, reject) => {
  stream.once('readable', onData);
  stream.on('error', onError);
  stream.on('end', done);

  function onData () {
   done();
   resolve(stream.read());
  }

  function onError (err) {
   done();
   reject(err);
  }

  function done () {
   stream.removeListener('readable', onData);
   stream.removeListener('error', onError);
   stream.removeListener('end', done);
  }
 })
}

'use strict';
const fs = require('fs');

let stream = fs.createReadStream('/Path/to/a/big/file');

function processSomeData (stream, callback) {
 stream.on('data', (data) => {
  // 对数据进行一些异步耗时操作
  setTimeout(() => console.log(data), 2000);
 });

 stream.on('end', () => {
  // ...
  callback()
 })
}

processSomeData(stream, () => console.log('end'));

function processSomeData (stream, callback) {
 let count = 0;
 let finished = 0;
 let isEnd = false;

 stream.on('data', (data) => {
  count++;
  // 对数据进行一些异步耗时操作
  setTimeout(() => {
   console.log(data);
   finished++;
   check();
  }, 2000);
 });

 stream.on('end', () => {
  isEnd = true;
  // ...
  check();
 })

 function check () {
  if (count === finished && isEnd) callback()
 }
}