我可以在fs.createWriteStream中使用forEach吗？

Question

I need to create .txt file which show the content of an array line by line. At the moment I am using the following script but file is being created but it is empty.

What could cause the problem?

  var wstream = fs.createWriteStream('myOutput.txt');
    [1,2,3,4].forEach(function(item){
       wstream.write(item, '\n'); 
    }.bind(this));
    wstream.end();

Answer 1

Yes , you can use .forEach() inside a stream write. Your issue has nothing to do with the use of .forEach() at all. Instead, you are passing the wrong arguments to .write() . It does not take two separate arguments that are both data for the stream like you are using it. The function signature for .write() is this:

writable.write(chunk[, encoding][, callback])

So, when you do this:

wstream.write(item, '\n'); 

your second argument is being interpreted as an encoding which does not work. In fact, it throws an exception which you should have been able to see.

You can, instead, change to this:

 wstream.write(item + '\n'); 

This overall script works:

const fs = require('fs');

var wstream = fs.createWriteStream('myOutput.txt');
[1,2,3,4].forEach(function(item){
   wstream.write(item + '\n'); 
});
wstream.end();

FYI, I've tried this code on my own computer with node 4.x and it works.

Answer 2

Your array is not a stream, so there's no need to use stream writing. You can just use fs.writeFile and use yourArrayOfLines.join('\\n') in as file content.

var lines = [.....];
fs.writeFile('myoutput.txt', lines.join('\n'), 'utf8');

done. Fewer lines, more obvious code behaviour (and note that the encoding is optional, it'll default to utf8 if you leave it off).