Answers for "async for js"

for await example

(async function() {
  for await (let num of asyncIterable) {
    console.log(num);
  }
})();

// 0
// 1
// 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.

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');
	}
}

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();

javscript async await explained

// Promise approach

function getJSON(){

    // To make the function blocking we manually create a Promise.
    return new Promise( function(resolve) {
        axios.get('https://tutorialzine.com/misc/files/example.json')
            .then( function(json) {

                // The data from the request is available in a .then block
                // We return the result using resolve.
                resolve(json);
            });
    });

}

// Async/Await approach

// The async keyword will automatically create a new Promise and return it.
async function getJSONAsync(){

    // The await keyword saves us from having to write a .then() block.
    let json = await axios.get('https://tutorialzine.com/misc/files/example.json');

    // The result of the GET request is available in the json variable.
    // We return it just like in a regular synchronous function.
    return json;
}

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();