async await promise javascript example

Example 1: nodejs promise async

// server.js
 
function square(x) {
  return new Promise(resolve => {
    setTimeout(() => {
      resolve(Math.pow(x, 2));
    }, 2000);
  });
}
 
async function layer(x)
{
  const value = await square(x);
  console.log(value);
}
 
layer(10);

Example 2: async await javascript

function hello() {
  return new Promise((resolve,reject) => {
    setTimeout(() => {
      resolve('I am adam.');
    }, 2000);
  });
}
async function async_msg() {
  try {
    let msg = await hello();
    console.log(msg);
  }
  catch(e) {
    console.log('Error!', e);
  }
}
async_msg(); //output - I am adam.

Example 3: js async await

/* Notes:
	1. written like synchronous code
    2. compatible with try/catch blocks
    3. avoids chaining .then statements
    4. async functions always return a promise
    5. function pauses on each await expression
    6. A non promise value is converted to 
       Promise.resolve(value) and then resolved
*/

// Syntax
// Function Declaration
async function myFunction(){
  await ... // some code goes here
}
  
// Arrow Declaration
const myFunction2 = async () => {
  await ... // some code goes here
}
  
 // OBJECT METHODS

const obj = {
	async getName() {
		return fetch('https://www.example.com');
	}
}

// IN A CLASS

class Obj {
	// getters and setter CANNOT be async
	async getResource {
		return fetch('https://www.example.com');
	}
}

Example 4: nodejs promise async

// Normal Function
function add(a,b){
  return a + b;
}
// Async Function
async function add(a,b){
  return a + b;
}

Example 5: javascript async await

// The await operator in JavaScript can only be used from inside an async function.
// If the parameter is a promise, execution of the async function will resume when the promise is resolved
// (unless the promise is rejected, in which case an error will be thrown that can be handled with normal JavaScript exception handling).
// If the parameter is not a promise, the parameter itself will be returned immediately.[13]

// Many libraries provide promise objects that can also be used with await,
// as long as they match the specification for native JavaScript promises.
// However, promises from the jQuery library were not Promises/A+ compatible until jQuery 3.0.[14]

async function createNewDoc() {
  let response = await db.post({}); // post a new doc
  return await db.get(response.id); // find by id
}

async function main() {
  try {
    let doc = await createNewDoc();
    console.log(doc);
  } catch (err) {
    console.log(err);
  }
}
main();

Example 6: async await js

fetch('coffee.jpg')
.then(response => {
  if (!response.ok) {
    throw new Error(`HTTP error! status: ${response.status}`);
  } else {
    return response.blob();
  }
})
.then(myBlob => {
  let objectURL = URL.createObjectURL(myBlob);
  let image = document.createElement('img');
  image.src = objectURL;
  document.body.appendChild(image);
})
.catch(e => {
  console.log('There has been a problem with your fetch operation: ' + e.message);
});