ES2015: Promise, Async/Await

• Promises are an alternative to callbacks for delivering the results of an asynchronous computation.

• A Promise is always in one of three mutually exclusive states: - Before the result is ready, the Promise is pending. - If a result is available, the Promise is fulfilled. - If an error happened, the Promise is rejected.

• A Promise is settled if “things are done” (if it is either fulfilled or rejected).

• A Promise is settled exactly once and then remains unchanged.

• Promise reactions are callbacks that you register with the Promise method then(), to be notified of fulfillment or a rejection.

• A thenable is an object that has a Promise-style then() method. Whenever the API is only interested in being notified of settlements, it only demands thenables (e.g. the values returned from then() and catch(); or the values handed to Promise.all() , Promise.allSettled(), Promise.race()), Promise.race()).

• Create a promise

• Consuming a Promise

• Other ways of creating Promises - Promise.resolve() - Promise.reject()

• Chaining Promises

• Promise anti-pattern: nested

• then always return a promise

• Async functions: always return a promise

• Await: works only inside async functions

• Can’t use await in regular functions

• await won’t work in the top-level code

• Error handling

• Too Sequential

• http://speakingjs.com/es5/index.html

• http://exploringjs.com/es6/index.html

• http://exploringjs.com/es2016-es2017/ch_async-functions.html

• http://exploringjs.com/es2018-es2019/toc.html

• http://eloquentjavascript.net/

• https://github.com/getify/You-Dont-Know-JS#titles