async.js

// returns promise.

function foo() {
  return new Promise(function(resolve, reject) {
    setTimeout(function() {
      if (Math.random() < .5) {
      	resolve(Math.random());
      } else {
        reject(new Error(Math.random()));
      }
    }, 1000);
  });
}

// async function.

async function bar() {
  console.log('this is bar.');
  while (true) {
    try {
      var ret = await foo();
      console.log(ret);
    } catch (e) {
      console.log(e);
    }
  }
}

// async function. (inline promise)

async function baz() {
  console.log('this is baz.');
  while (true) {
    try {
      var ret = await new Promise(function(resolve, reject) {
        setTimeout(function() {
          if (Math.random() > 0.5) {
            resolve('resolve');
          } else {
            reject(new Error('Error'));
          }
        }, Math.random() * 1000);
      });
      console.log(ret);
    } catch (e) {
      console.log(e);
    }
  }
}

// call async functions.

console.log('async function bar() calling...');
console.log('bar', bar());
console.log('async function baz() calling...');
console.log('baz', baz());

console.log

$ babel-node test.js 
async function bar() calling...
this is bar.
bar Promise {
  _d: 
   { p: [Circular],
     c: [],
     a: undefined,
     s: 0,
     d: false,
     v: undefined,
     h: false,
     n: false } }
async function baz() calling...
this is baz.
baz Promise {
  _d: 
   { p: [Circular],
     c: [],
     a: undefined,
     s: 0,
     d: false,
     v: undefined,
     h: false,
     n: false } }
[Error: Error]
resolve
0.7497521410696208
resolve
[Error: Error]
resolve
0.1544457538984716
[Error: Error]
[Error: 0.8831553251948208]
[Error: Error]
0.07748340792022645
resolve
resolve
0.4588852066081017
resolve
[Error: Error]
[Error: 0.8220234394539148]
[Error: Error]
[Error: 0.5263843222055584]
resolve
[Error: Error]
[Error: Error]
0.5478959816973656
^C