promise_functions.js

// then-catch-final(then)
const taskA = () => {
  console.log("Task A")
  throw new Error("throw Error at taskA")
}
const taskB = () => {
  console.log("Task B")  // does not be call
}
const onRejected = (error) => {
  console.error(error)  // => "throw Error at taskA"
}
const finalTask = () => {
  console.log("Final Task")
}

Promise.resolve()
  .then(taskA)
  .then(taskB)
  .catch(onRejected)
  .then(finalTask)

// onload or dom content loaded
const onReady = () => {
  return new Promise((resolve) => {
    const readyState = document.readyState
    if (
      readyState === "interactive" ||
      readyState === "complete"
    ) {
      resolve()
    } else {
      window.addEventListener("DOMContentLoaded", resolve)
    }
  })
}
onReady().then(() => {
  console.log("DOM fully loaded and parsed")
})
console.log("==Starting==")