pump模块的学习-metamask

pump = require('pump')

pump简介

https://github.com/terinjokes/gulp-uglify/blob/master/docs/why-use-pump/README.md#why-use-pump

当使用来自Node.js的管道时，错误不会通过管道流向前传播，如果目标流关闭，源流也不会关闭。pump模块将这些问题规范化，并在回调中传递错误。

pump可以使我们更容易找到代码出错位置。

A common gulpfile example

A common pattern in gulp files is to simply return a Node.js stream, and expect the gulp tool to handle errors.

gulp文件中的一个常见模式是简单地返回一个Node.js流，并期待gulp工具能处理错误

// example of a common gulpfile
var gulp = require('gulp');
var uglify = require('gulp-uglify');

gulp.task('compress', function () {
  // returns a Node.js stream, but no handling of error messages
  return gulp.src('lib/*.js')
    .pipe(uglify())
    .pipe(gulp.dest('dist'));
});

There’s an error in one of the JavaScript files, but that error message is the opposite of helpful. You want to know what file and line contains the error. So what is this mess?

这里有一个错误在某个JavaScript文件中，但是这些错误信息并没有起到什么作用。我们真正想要知道的是哪个文件的哪一行出现了这些错误。

When there’s an error in a stream, the Node.js stream fire the 'error' event, but if there’s no handler for this event, it instead goes to the defined uncaught exception handler. The default behavior of the uncaught exception handler is documented:

当在流中出现了错误时，将会触发'error'事件，但是如果这里的事件没有handler的话，它将会定义一个没有捕捉的异常handler，如下文档说明：

By default, Node.js handles such exceptions by printing the stack trace to stderr and exiting.默认情况下,Node.js通过将堆栈跟踪打印到stderr和退出来处理这些异常

Handling the Errors

Since allowing the errors to make it to the uncaught exception handler isn’t useful, we should handle the exceptions properly. Let’s give that a quick shot.

即然如果不处理异常将默认为uncaught exception handler（这是没有用的），那么我们就应该恰当地对异常进行处理

var gulp = require('gulp');
var uglify = require('gulp-uglify');

gulp.task('compress', function () {
  return gulp.src('lib/*.js')
    .pipe(uglify())
    .pipe(gulp.dest('dist'))
    .on('error', function(err) { //添加一个异常处理
      console.error('Error in compress task', err.toString());
    });
});

Unfortunately, Node.js stream’s pipe function doesn’t forward errors through the chain, so this error handler only handles the errors given by gulp.dest. Instead we need to handle errors for each stream.

但是这个异常处理是不会通过链来传递错误的，所以它只会处理来自 gulp.dest的错误。那么如果我们要处理每一个流的错误的话，就要像下面一样，每个流都进行错误处理

var gulp = require('gulp');
var uglify = require('gulp-uglify');

gulp.task('compress', function () {
  function createErrorHandler(name) {
    return function (err) {
      console.error('Error from ' + name + ' in compress task', err.toString());
    };
  }

  return gulp.src('lib/*.js')
    .on('error', createErrorHandler('gulp.src'))
    .pipe(uglify())
    .on('error', createErrorHandler('uglify'))
    .pipe(gulp.dest('dist'))
    .on('error', createErrorHandler('gulp.dest'));
});

This is a lot of complexity to add in each of your gulp tasks, and it’s easy to forget to do it. In addition, it’s still not perfect, as it doesn’t properly signal to gulp’s task system that the task has failed. We can fix this, and we can handle the other pesky issues with error propogations with streams, but it’s even more work!

这样就会变得很复杂，而且你也很容易就忘记这么做。所以我们需要使用pump

Using pump

The pump module is a cheat code of sorts. It’s a wrapper around the pipe functionality that handles these cases for you, so you can stop hacking on your gulpfiles, and get back to hacking new features into your app.

它是用来处理上面这些情况的pipe的包装器，这样您就可以停止对您的gulpfile文件进行黑客攻击，并重新对您的应用程序进行黑客攻击

var gulp = require('gulp');
var uglify = require('gulp-uglify');
var pump = require('pump');

gulp.task('compress', function (cb) {
  pump([
      gulp.src('lib/*.js'),
      uglify(),
      gulp.dest('dist')
    ],
    cb //回调函数
  );
});

The gulp task system provides a gulp task with a callback, which can signal successful task completion (being called with no arguments), or a task failure (being called with an Error argument). Fortunately, this is the exact same format pump uses!

Now it’s very clear what plugin the error was from, what the error actually was, and from what file and line number.

这样我们就能够看见是什么触发了error，在哪个文件的哪一行

这只是一个简单的了解，如果想要更深入的学习请自学https://github.com/pump-io/pump.io

之后如果看了这部分再写出来