Simple ES6 Async Example: Rewriting a promise chain with an async function

asynce-example-simple-fetchdata.js

/*
 *  Using An API that returns a Promise will 
 *  result in a promise chain, and it splits 
 *  the function into many parts.
 *
 *    (for example...)
 */
function getProcessedData(url) {
  return downloadData(url) // returns a promise
    .catch(e => {
      return downloadFallbackData(url)  // returns a promise
    })
    .then(v => {
      return processDataInWorker(v); // returns a promise
    });
}

// ============================================================


/* However, it can be rewritten with a single async function as follows: */

async function getProcessedData(url) {
  let v;
  try {
    v = await downloadData(url); 
  } catch(e) {
    v = await downloadFallbackData(url);
  }
  return processDataInWorker(v);
}

//--------------------------------------------------------
//  Note that in the above example, 
//  there is no await statement on the return statement, 
//  because the return value of an async function is 
//  implicitly wrapped in Promise.resolve.
//--------------------------------------------------------

// Source: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function