createWriteStream vs writeFile?

Question

What is the basic difference between these two operations ?

someReadStream.pipe(fs.createWriteStream('foo.png'));

vs

someReadStream.on('data', function(chunk) { blob += chunk } );
someReadStream.on('end', function() { fs.writeFile('foo.png', blob) });

When using request library for scraping, I can save pics (png, bmp) etc.. only with the former method and with the latter one there is same gibbersh (binary) data but image doesn't render.

How are they different ?

Answer 1

When you are working with streams in node.js you should prefer to pipe them.

According to Node.js’s stream-event docs, data events emit either buffers (by default) or strings (if encoding was set).

When you are working with text streams you can use data events to concatenate chunks of string data together. Then you'll be able to work with your data as one string.

But when working with binary data it's not so simple, because you'll receive buffers. To concatenate buffers you use special methods like Buffer.concat. It's possible to use a similar approach for binary streams:

var buffers = [];
readstrm.on('data', function(chunk) {
    buffers.push(chunk);
});
readstrm.on('end', function() {
    fs.writeFile('foo.png', Buffer.concat(buffers));
});

You can notice when something goes wrong by checking the output file's size.