wallet-core/node_modules/fs-extra/docs/fs-read-write.md

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:

fs.read()

// 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)
}

fs.write()

// 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)
}