Promise and aysnc/await demo

await_test.js

/*
 * Promise and async/await function
 */
'use strict';

// type-1
// function(resolve) {}
function action1(msg) {
  return new Promise(
    function(resolve) {
      setTimeout(function() {
        resolve(msg);
        console.log('action1:'+msg); 
      }, 1000);
    }
  )
}

// type-2
// resolve => {}
function action2(msg) {
  return new Promise(resolve => {
    setTimeout(() => { 
      resolve(msg);
      console.log('action2:'+msg)
    }, 1000);
  });

}

function action3(msg) {
  return new Promise(resolve => {
    setTimeout(() => { 
      resolve(msg);
      console.log('action3:'+msg)
    }, 1000);
  });

}

async function action4() {
  let r1 = await action1('a1');
  let r2 = await action2('a2');
  return (r1+':'+r2);
}

// action4 vs action5
async function action5() {
  let r1 = action1('a1');
  let r2 = action2('a2');
  await r1;
  await r2;
  return r2;
  //return {r1, r2};
}

function getUserData() {
  return new Promise(resolve => {
    let user = {
      name: "jacky",
      mobile: "0933010234",
      email: "[email protected]"
    }
    setTimeout(() => {
      resolve(user);
      console.log('getUesrData');
    }, 1000);
  })
}

function main1() {
  console.log('main1');
  action1('a1')
    .then(() => action2('a2'))
    .then(() => action3('a3'))
}

function main2() {
  console.log('main2');
  action1('pass from a1')
    .then((msg) => action2(msg))
    .then((msg) => action3(msg))
}

async function main3() {
  console.log('main3');
  await action1('a1');
  await action2('a2');
  await action3('a3');
}

async function main4() {
  console.log('main4');
  let msg = await action1('pass from a1');
  await action2(msg);
  await action3(msg);
}

async function main5() {
  await action1('a1');
  let user = await getUserData();
  await action2(user.email);
  console.log('done5');
}

async function main6() {
  let r = await action4();
  console.log('main6:'+r);
  console.log('done');
}

async function main7() {
  let r2 = await action5();
  console.log('r2:'+r2);
  console.log('done');
}

async function main8() {
  for (let i = 0; i<10; i++) {
    await action1('a1');
  }
  console.log('done');
}

async function main9() {
  let arr = [];
  for (let i=0; i<10; i++) {
    arr.push(action1('a'+i));
  }
  console.log('parallel tasks')
  for (let j=0; j<10; j++) {
    await arr[j];
  }
  console.log('done');
}

console.log('start');

//main1();
//main2();
//main3();
//main4();
//main5();
//main6();
//main7();
//main8();
main9();