Gather the output

[sindresorhus]

Currently you can do the following if you want the output of multiple calls:

var output = [];
hookStd(str => output.push(str));

// when done logging you can use the `calls` array.

Would be nicer if it did this automagically and offered the output somehow.

Maybe like this?

// callback is now optional
const std = hookStd();

console.log('foo');
console.log('bar');

std.unhook();

console.log(std.output);
//=> 'foo\nbar\n'

@jamestalmage @sotojuan Thoughts? What should the API look like?

[sotojuan]

That would definitely make multiline output easier 👍 I would argue that's what some users would expect out of the box anyway.

[vadimdemedes]

Interesting module. I'd suggest unhook.stdout and unhook.stderr instead of one unhook.output. Otherwise, from the first impression, looks fine ;)

[Qix-]

Not sure about your last example (unhook is undefined), but I think I get it.

I'd almost want to see something more from this. Being able to hook or filter would be awesome.

const std = hookStd();

std.on('out', str => str.replace(/\n/g, '\n\t'));
std.on('err', str => str.replace(/\n/g, '\n!!\t'));

// or more practically
import chalk from chalk;
std.on('err', str => chalk.bright.red(str));

std.get('out'); // original output contents
std.get('err'); // original output contents

// same could be applied to 'in' but I couldn't think of an example off the top of my head.

Maybe it could also hook fs.write(1, ...) and fs.write(2, ...) as well as fs.read(0, ...) for completeness.

[sindresorhus]

Interesting module. I'd suggest unhook.stdout and unhook.stderr instead of one unhook.output.

👍

Not sure about your last example (unhook is undefined), but I think I get it.

Typo. Fixed.

std.on('out', str => str.replace(/\n/g, '\n\t'));
std.on('err', str => str.replace(/\n/g, '\n!!\t'));

Why events?

You can already do this with hookStd(str => str.replace(/\n/g, '\n\t'));

Maybe it could also hook fs.write(1, ...) and fs.write(2, ...) as well as fs.read(0, ...) for completeness.

Is 1 the stdout fd? I don't think that works on Windows anyways.

[jamestalmage]

Do you see this as primarily a test tool? If so, would it be valuable to provide convenience methods for accessing individual calls / lines?

// this would be one call but two lines
process.stdout.write('foo\nbar')

[sindresorhus]

@jamestalmage Yeah, was thinking about that. Could be an option. ?

[jamestalmage]

Could be an option

👍

[Qix-]

Why events?

Hooks are usually pretty event driven, and events are a good way to break up similar functionality with different inputs, optionally. I might want to subscribe to just stderr. How would I do that with a simple constructor? null?

Is 1 the stdout fd? I don't think that works on Windows anyways.

Yes; 0 = in, 1 = out, 2 = err. Technically more FDs can be assigned but that's archaic and edge-casey.

Pretty sure libuv abstracts this on windows (and I wouldn't be surprised if windows does work like that, given the C standard and whatnot).

Other fd's are pretty uncommon to use via output methods. Technically you could do this:

(echo "require('fs').createReadStream(null, {fd:3}).pipe(process.stdout);" | node) 3<<< "hello, world"

[sindresorhus]

Hooks are usually pretty event driven, and events are a good way to break up similar functionality with different inputs, optionally.

But your example won't work with events as events are async and can't take a return value. So modifying the output like you're doing in your example wouldn't work.

I might want to subscribe to just stderr. How would I do that with a simple constructor? null?

See how I already solve it. Main export for both. Sub-prop for specific stream.

Pretty sure libuv abstracts this on windows (and I wouldn't be surprised if windows does work like that, given the C standard and whatnot).

They might, but I've honestly never seen this used and I don't think I want to bother adding support for it until there's demand.

[Qix-]

But your example won't work with events as events are async and can't take a return value. So modifying the output like you're doing in your example wouldn't work.

Derp, you're right.

Main export for both. Sub-prop for specific stream.

That doesn't seem intuitive to me, IMO, but I can't think of a better solution.

They might, but I've honestly never seen this used and I don't think I want to bother adding support for it until there's demand.

It's proper FD stuff. It'd be super complete if you did.

---

For giggles, I wondered if writing to process.stdout called either write or writeSync with the fd of 1.

It doesn't.

^{fd 20, as you can see, is just its REPL history}

So it's up to you if you want to support it. It would be correct functionality, as anything written to 1 or 2 wouldn't be hooked by this library.

[sindresorhus]

That doesn't seem intuitive to me, IMO, but I can't think of a better solution.

I guess I could have dropped the main export and done an hookStd.all export instead, but I don't see how that's any better.

So it's up to you if you want to support it. It would be correct functionality, as anything written to 1 or 2 wouldn't be hooked by this library.

I've yet to see anyone use that in Node.js and I don't see why they would when we have a better way.

[Qix-]

I don't see why they would when we have a better way

Maybe not explicitly, but if you have a FD configuration and you just want to write to standard output instead of a file descriptor for an actual file, you'd just specify 1 and not have to change any functionality. It's somewhat common practice in C coding and since Node is just a loose javascript wrapper around Unix functionality it would make sense (to me, anyway).

But I am just a C programmer in a Javascript programmer's body. 👻