How can you avoid callback hells?

getData(function(a) {
  getMoreData(a, function(b) {
    getMoreData(b, function(c) {
      getMoreData(c, function(d) {
        getMoreData(d, function(e) {
          // ...
        })
      })
    })
  })
})

Answer

Refactoring the functions to return promises and using async/await is usually the best option. Instead of supplying the functions with callbacks that cause deep nesting, they return a promise that can be awaited and will be resolved once the data has arrived, allowing the next line of code to be evaluated in a sync-like fashion.

The above code can be restructured like so:

async function asyncAwaitVersion() {
  const a = await getData()
  const b = await getMoreData(a)
  const c = await getMoreData(b)
  const d = await getMoreData(c)
  const e = await getMoreData(d)
  // ...
}

There are lots of ways to solve the issue of callback hells:

• Modularization: break callbacks into independent functions

• Use a control flow library, like async

• Use generators with Promises

• Use async/await (from v7 on)

Good to hear

• As an efficient JavaScript developer, you have to avoid the constantly growing indentation level, produce clean and readable code and be able to handle complex flows.

Additional links

• Avoiding Callback Hell in Node.js
• Asynchronous JavaScript: From Callback Hell to Async and Await