async.js code example

Example 1: 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 2: async

function resolveAfter2Seconds() {
  return new Promise(resolve => {
    setTimeout(() => {
      resolve('resolved');
    }, 2000);
  });
}

async function asyncCall() {
  console.log('calling');
  const result = await resolveAfter2Seconds();
  console.log(result);
  // expected output: 'resolved'
}

asyncCall();

Example 3: 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);
});