Callback in javascript

const fs = require('fs')
fs.readFile('/etc/passwd', (err, data) => {
  if (err) {
    console.error(err)
    return
  }
  console.log(data.toString())
})

Sử dụng callback rất hạn chế ví dụ :

fs.readFile(fileA, function (err, data) {
  fs.readFile(fileB, function (err, data) {
    // ...
  })
}

Có thể bạn đã miss một số snippets code

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Now we can use rest on the properties of an Object. It allows us to explicitly extract certain named variables, and assign any uncalled variables into a catchall Object.

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