blink/tutorials/1_promises.js

49 lines
1.5 KiB
JavaScript

// https://javascript.info/promise-basics
/*
The function passed to Promise is called "executor". When Promise gets
created, the executor gets executed.
When the Promise ends, it should either call the "resolve" or "reject"
callbacks:
resolve(value) — if the job is finished successfully, with result value.
reject(error) — if an error has occurred, error is the error object.
Remember that Promises are not intrensically asyncronous
*/
const promise = new Promise(function (resolve, reject) {
setTimeout(() => resolve('done'), 500);
});
/*
The first argument of .then is a function that runs when the promise is resolved and receives the result.
The second argument of .then is a function that runs when the promise is rejected and receives the error.
*/
promise.then(
result => console.log('The operation was successful. It returned ' + result),
error => console.log('The operation was not successful: ' + error)
);
/*
Or we can pass only one argument if we're interested only in a positive result
*/
promise.then(
result => console.log('The operation was successful. It returned ' + result)
);
/*
Or we can pass only one argument to the method "catch" if we're interested
in negative results only.
promise.catch internally just calls promise.then(null, f)
*/
promise.catch(
error => console.log(error)
);
/*
finally gets always called
*/
promise.finally(
() => console.log('The execution has terminated. Bye')
);