The Promise of await / async

await-async.js

// async / await

/**
 * Resolve a truthy value, reject a falsy value.
 * @param {any} value Any Javascript primative type.
 * @param {Number} timeout Time n milliseconds before function returns.
 * @returns {Promise} a Promise.
 */
let isTruthy = function(value, timeout) {
  return new Promise((resolve, reject) => {
    window.setTimeout(() => {
      value = value ? true : false;
      if(value === true) {
        return resolve(value);
      } else {
        return reject(value);
      }
    }, timeout);
  });
};

let getResult = async function(value) {
  setTimeout(() => console.info(`${value} 2`), 2000);
  setTimeout(() => console.info(`${value} 3`), 3000);
  setTimeout(() => console.info(`${value} 1`), 1000);
  try {
    let result = await isTruthy(value, 3100);
    console.info(`try result '${value}': ${result}`);
  } catch(error) {
    console.warn(`catch result: '${value}': ${error}`);
  }
}

getResult('yes');
getResult(0);

/* Improvements:
 * - Code is subjectively easier to reason about.
 * - No need for `.then()` or `.catch()` in `getResult`.
 * - getResult can use try / catch to handle Promise rejection errors in `isTruthy`
 * - Debugging is easier, `.then` and `.catch` dont accept break-points as the
 *     body is an expression, not a function body.
 */

promises.js

// Promises

/**
 * Resolve a truthy value, reject a falsy value.
 * @param {any} value Any Javascript primative type.
 * @param {Number} timeout Time n milliseconds before function returns.
 * @returns {Promise} a Promise.
 */
let isTruthy = function(value, timeout) {
  return new Promise((resolve, reject) => {
    window.setTimeout(() => {
      value = value ? true : false;
      if(value === true) {
        return resolve(value);
      } else {
        return reject(value);
      }
    }, timeout);
  });
};

let getResult = function(value) {
  setTimeout(() => console.info(`${value} 2`), 2000);
  setTimeout(() => console.info(`${value} 3`), 3000);
  setTimeout(() => console.info(`${value} 1`), 1000);
  let resultPromise = isTruthy(value, 3100);
  resultPromise
    .then(result => console.info(`then result '${value}': ${result}`))
    .catch(result => console.warn(`catch result: '${value}': ${result}`));
}

getResult('yes');
getResult(0);