async await example

Example 1: async await

const data = async ()  => {
  const got = await fetch('https://jsonplaceholder.typicode.com/todos/1');
  
  console.log(await got.json())
}

data();

Example 2: async await in forloops

// Series loop
async (items) => {
  for (let i = 0; i < items.length; i++) {
  	
    // for loop will wait for promise to resolve
    const result = await db.get(items[i]);
    console.log(result);
  }
}

// Parallel loop
async (items) => {
  let promises = [];
  
  // all promises will be added to array in order
  for (let i = 0; i < items.length; i++) {
    promises.push(db.get(items[i]));
  }
  
  // Promise.all will await all promises in the array to resolve
  // then it will itself resolve to an array of the results. 
  // results will be in order of the Promises passed, 
  // regardless of completion order
  
  const results = await Promise.all(promises);
  console.log(results);
}

Example 3: async await

async function showAvatar() {

  // read our JSON
  let response = await fetch('/article/promise-chaining/user.json');
  let user = await response.json();

  // read github user
  let githubResponse = await fetch(`https://api.github.com/users/${user.name}`);
  let githubUser = await githubResponse.json();

  // show the avatar
  let img = document.createElement('img');
  img.src = githubUser.avatar_url;
  img.className = "promise-avatar-example";
  document.body.append(img);

  // wait 3 seconds
  await new Promise((resolve, reject) => setTimeout(resolve, 3000));

  img.remove();

  return githubUser;
}

showAvatar();

Example 4: how to make an async function

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

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

asyncCall();

Example 5: 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 6: 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');
	}
}