javascript - Node 和惰性 : How do I know when it's done?

Question

我需要逐行读取文件，并相应地更改变量。我通常会用 PHP 编写此...但我决定接受挑战。

我写道:

fs = require('fs');
Lazy = require('lazy');
path = require('path');

files = fs.readdirSync('.');
var software = {};


files.forEach( function(fileName){


  var m; 
  if( m = fileName.match(/^(.*)\.txt$/) ){
    name = m[1];

    console.log("Processing file: " + fileName);
    software[name] = {};
    console.log("Software 1: %j",software);

    var section = 'unset';
    new Lazy(fs.createReadStream(fileName)).lines.forEach(
      function(line){
        var m;
        line = line + '';
        if( m = line.match(/^([a-zA-Z_]*):$/)){
          section = m[1];
          software[name][section] = '';
          console.log("Switching to section " + m[1]);
          console.log("Software 2: %j",software);
        } else if (line == '.'){
          section = 'unset'
        } else if (line == ''){
          section = 'unset'
        } else { 
          console.log("LINE: " + line) ;
          software[name][section] = software[name][section] + line + "\n";
          console.log("Software 3: %j",software);
        }
      }

    );   
  }

});

console.log("Software 4: %j",software);

除了代码非常丑陋和非常未优化之外，我还遇到了问题，因为当最后一行打印出来时，“软件”变量还没有填充!我猜 Lazy 是异步的。所以，它基本上有效，但“在某个时候”。这很好，但是......当填充软件变量的重要循环实际完成时，我应该在哪里编写代码？!？

根据要求:要玩的数据!

只需创建“something.txt”并写入:

name:
Name 1
.

Option 1:
Value 1
.

Option 2:
Value 2
.

Option 3:
Multi
Line
Value
.

Another_section:
Again
.

雇佣兵。

Answer 1

库返回的 Lazy 实例是 EventEmitters ，并在完成“一组”操作时发出名为 pipe 的事件:

new Lazy(
  ...
).on('pipe', function() {
  // all done
});

修改您的代码以使用此事件会导致(唯一的变化在底部附近):

fs = require('fs');
Lazy = require('lazy');
path = require('path');

files = fs.readdirSync('.');
var software = {};


files.forEach( function(fileName){


  var m;
  if( m = fileName.match(/^(.*)\.txt$/) ){
    name = m[1];

    console.log("Processing file: " + fileName);
    software[name] = {};
    console.log("Software 1: %j",software);

    var section = 'unset';
    new Lazy(fs.createReadStream(fileName)).lines.forEach(
      function(line){
        var m;
        line = line + '';
        if( m = line.match(/^([a-zA-Z_]*):$/)){
          section = m[1];
          software[name][section] = '';
          console.log("Switching to section " + m[1]);
          console.log("Software 2: %j",software);
        } else if (line == '.'){
          section = 'unset'
        } else if (line == ''){
          section = 'unset'
        } else {
          console.log("LINE: " + line) ;
          software[name][section] = software[name][section] + line + "\n";
          console.log("Software 3: %j",software);
        }
      }

    ).on('pipe', function() {
      console.log("Software 4: %j",software);
    });
  }

});

[编辑] 回答有关我如何找到此信息的问题:

我确实查看了the source file for the project ;我知道该库有一个 sum 方法，可以链接到 Lazy 的实例以在最后总结所有内容； code for that method调用 foldr，以及 code for that method监听名为 pipeName 的事件，默认为 in line 22作为管道。