Sequencing async functions with callbacks

example.js

utils.sequence([
  (ready) => connection.query(createPersonTableSQL, (error, results, fields) => {
    ready()
  }),
  (ready) => connection.query(createPortfolioTableSQL, (error, results, fields) => {
    ready()
  }),
  (ready) => connection.query(createDebtTableSQL, (error, results, fields) => {
    ready()
  }),
  (ready) => connection.query(createCalendarTableSQL, (error, results, fields) => {
    ready()
  }),
  (ready) => connection.query(createPaymentTableSQL, (error, results, fields) => {
    ready()
  })
], () => {
  console.log("Migration finished")
  completed()
})

sequence.js

/**
 * Allows to call functions with callbacks in sequence
 * @param {function[]} arr 
 * @param {function} completed 
 */
function sequence(arr, completed) {
  let index = -1

  let ready = function() {
    if (index !== arr.length - 1) {
      callNext()
    } else {
      if (completed)
        completed()
    }
  }

  var callNext = function() {
    index++
    arr[index](ready)
  }
  
  callNext()
}