Add ignore option about node-watch

[wmertens]

Lol, I'm implementing this ;) I tried implementing the filter optimization as-is, but then I realized via the tests that it would break a lot of current installs, and adding ignore works better. I'll do a pr soon

[Krinkle]

I think this is quite similar to the filter option that exists already.

The main difference is that the proposal here would also save (fallback) resources by not watching matching subdirectories in the first place. There is issue #93 which proposes to apply that to the filter option which might be simpler.

For the use case of supporting full gitignore glob patterns, I think it would make sense to document how to use existing libraries for that. E.g. this can be done with one line of code by using picomatch (or minimatch) from the filter option.

[wmertens]

@Krinkle actually, I started by implementing filter but quickly ran into problems with, IIRC, not being able to express ignoring the folder but not subfolders. I don't quite remember but implementing ignore instead made it backwards-compatible and solved the issue.

[yuanchuan]

Revisiting the problem a few months later, I suppose it's not a good idea to implement the ignore functionality inside node-watch since there are so many packages for this already. Add another similar option by name will confuse people to use it too.

[wmertens]

@yuanchuan the reason I'm implementing this is to optimize large trees - node-watch shouldn't watch subdirectories that that aren't interesting.

Adding ignore is the only way I can think of to do this without breaking the API...

[yuanchuan]

@wmertens How about this way? See #101

If an explicit skip string is returned, it will skip the sub-directories.

[yuanchuan]

So the ignore can be implemented like this with the skip flag added in #101 and the package ignore.

const fs = require('fs');
const watch = require('node-watch');
const ignore = require('ignore');

const matchGitIgnore = (() => {
  const ig = ignore().add(fs.readFileSync('./.gitignore', 'utf8'));
  return name => ig.ignores(name);
})();

let options = {
  recursive: true,
  filter(name, skip) {
    if (matchGitIgnore(name)) return skip;
    return (/\.js$/.test(name));
  }
};

watch('./', options, console.log);

Or another simpler way:

const watch = require('node-watch');
const ignore = require('ignore');

function matchIgnoreList(list) {
  const ig = ignore().add(list);
  return name => ig.ignores(name);
}

let matchIgnore = matchIgnoreList(['node_modules', '.git']);

let options = {
  recursive: true,
  filter(name, skip) {
    if (matchIgnore(name)) return skip;
    return true;
  }
};

watch('./', options, console.log);