Promises Ex1

delay-error.js

/*
 YDKJS Async and Performance ch 3:Promises "Chain Flow" pg 81

 Generalized chain illustration, a delay-Promise creation
 utility with error handling and substituted resolution message/
 error recovery.
 */

'use strict';

function delay(time) {
    // Wrap setTimeout in a promise, making it 'thenable'
    // This technique can be applied to non-promise utilities
    // such as an ajax() call.
    return new Promise(function (resolve, reject) {
        setTimeout(resolve, time);
    });
}

// step 1:
console.log('step 1');
delay(0)
    // step 2:
    .then(function (response1) {
        console.log('step 2 - error');
        delay.bar(); // undefined, error!
        // never gets here
        return delay(100);
    })
    // step 3:
    .then(
    function fulfilled(response2) {
        console.log('step 3 - fulfilled');
        // never gets here
    },
    // rejection handler to catch the error
    function rejected(err) {
        console.log('step 3 - rejected');
        console.log(err);
    // `TypeError` from `delay.bar()` error reported
        return 42; // recovery action
    })
    // step 4:
    .then(function (msg) {
        console.log('step 4 - recovered');
        console.log(msg); // 42 - error recovered
    });