Add pathExists()

[RyanZim]

This is my approach at resolving #145.

fs.exists is broken. We're a drop-in replacement for fs, so we can't fix it.

We can make a new method that acts like fs.exists should have behaved all along. I've named it pathExists().

I also aliased fs.existsSync to fs.pathExistsSync for consistency.

Example Usage

const fs = require('fs-extra')

const file = '/tmp/this/path/does/not/exist/file.txt'
// Promise usage:
fs.pathExists(file)
  .then(exists => console.log(exists)) // => false
// Callback usage:
fs.pathExists(file, (err, exists) => {
  console.log(err) // => null
  console.log(exists) // => false
})

[coveralls]

Coverage increased (+0.08%) to 86.812% when pulling 0e7d1b3 on path-exists into 33b7f84 on develop.

[manidlou]

LGTM! 👍

[jprichardson]

I like it, nice work @RyanZim!

[jaredallard]

I'm interested in why fs-extra doesn't support using the not-broken fs.exists when accessing it via a promise. Seems like you could make it drop-in compatible via the promise version and keep using the broken version when NOT accessing it via a promise. Maybe I'm missing something though

[RyanZim]

@jaredallard We do promisify fs.exists, and still offer the broken fs.exists to callback users. However, we encourage the use of fs.pathExists, since it doesn't use deprecated Node APIs, and the callback version behaves correctly.

[jaredallard]

@RyanZim Yes, I know fs.exists is promisified, but I'm wondering why not have it point to/use the solution that pathExists implements, since you can literally rewrite fs.exists -> fs.pathExists right now. Since how fs.exists behaves (in it's broken way) is somewhat how it's consumed as a promise (catch is used as the err instead).

TL;DR
The normal callback way should point to the broken one for compat, but the fs.exists promise version could be the same as the current fs.pathExists AFAIK (for people who don't upgrade to pathExists (which isn't a standard api anyways))

[RyanZim]

The normal callback way should point to the broken one for compat, but the fs.exists promise version could be the same as the current fs.pathExists

Yes; that's the way things currently work.