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About `fs.read()` & `fs.write()`

`fs.read()` & `fs.write()` are different from other `fs` methods in that their callbacks are called with 3 arguments instead of the usual 2 arguments.

If you're using them with callbacks, they will behave as usual. However, their promise usage is a little different. `fs-extra` promisifies these methods like `util.promisify()` (only availible in Node 8+) does.

Here's the example promise usage:

# <tt>fs.read()</tt>

// Basic promises
fs.read(fd, buffer, offset, length, position)
.then(results => {
console.log(results)
// { bytesRead: 20, buffer: <Buffer 0f 34 5d ...> }
})
// Async/await usage:
async function example () {
const { bytesRead, buffer } = await fs.read(fd, Buffer.alloc(length), offset, length, position)
}

# <tt>fs.write()</tt>

// Basic promises
fs.write(fd, buffer, offset, length, position)
.then(results => {
console.log(results)
// { bytesWritten: 20, buffer: <Buffer 0f 34 5d ...> }
})
// Async/await usage:
async function example () {
const { bytesWritten, buffer } = await fs.write(fd, Buffer.alloc(length), offset, length, position)
}