Updated on 22 May 2019 | 4 Min Read
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Node js is a cross-platform and open-source framework and provides n number of useful JavaScript modules that enhances the coding experience and makes web applications development simpler. A few key concepts that are listed in node js interview questions on our website can give you a good insight of all you need to prepare for interviews on node js. It is easy to install, learn, and practice.

What are async-await and Promise?

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Async / await

In real-life applications, a lot of nested callback functions are needed. Each asynchronous call can then become a pain and lead to confusions. Using async/await simplifies the process of writing nested promises that would otherwise be confusing. It creates a non-blocking code. To make a function async, we need to add the keyword async to the function definition, so that the function returns an async object.

Example

async function sum (a, b){
   return a+b;
}

Promise

To know how to use async/await, we first need to understand how to write code using promises. We have discussed with command in detail in our node js interview questions and answers section.

How to use async-await with promise?

Let us go through the steps to use async-await with a promise.

# Step 1

You have to install async with npm install async command.

# Step 2

Call or import the async in the file where you want to use async.
var async = require("async");

# Step 3

Step3. Make an async function and call await function inside async function.
let phoneChecker = async function (req, res){
    const result = await phoneExistOrNot();
}

exports.phoneChecker = phoneChecker;
Await will work only under async function.

# Step 4

Now you can write your business logic in await function.
let phoneExistOrNot = async function (req, res){
    return new Promise(function(resolve, reject) {
       db.query('select name, phone from users where phone = 123456789 ', function (error, result) {
          if(error) {
             reject(error);
             console.log('Error');
          } else {
             resolve(result);
             console.log('Success');
          }
      })
   });
}

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Why we need async-await and promise?

Though just using promise serves the purpose, imagine having more and more nesting – the code would break all the coding standards and at some point, be beyond comprehension. Our collection of advanced node js interview questions explains this point in a more detailed manner.

This is why we need async/await – to eliminate the wrong output issue as well as make our code more straightforward and more robust.

The benefit of async-await and promise

It depends on a developer whether to choose promise or async/await in their code. However, all async functions implicitly return a promise, and every function that returns a promise is an async function. Using a combination of promise and async/await, you can get the benefits of both.

  • You can create multiple small async functions that can run parallelly if required. If they need to run one after the other, use await.
  • The code looks more straightforward and easy to read.
  • Easier to debug.
  • The code with async/await behaves more like synchronous code.
  • Both synchronous and asynchronous errors can be handled using try/catch.
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