While knowing how to construct a promise is useful, most of your interactions with promises will be spent consuming (or using) Promises
Put another way, you’ll be handling Promise objects returned to you as the result of an asynchronous operation
These promises will start off pending but must settle eventually
Promise objects offer a .then() function that allows us to dictate what should happen after the promise settles
.then() is a function that takes two callback functions as arguments; when the promise settles, the appropriate handler will be invoked with that settled value
onFulfilled: The first handler is the success handler, and it should contain the logic for the promise resolving
onRejected: The second handler is the failure handler, and it should contain the logic for the promise rejecting
let promise = new Promise(function(resolve, reject) {
setTimeout(() => resolve("done!"), 1000)
})
// resolve runs the first function in .then()
promise.then(
result => console.log(result), // shows "done!" after 1 second
error => console.log(error) // doesn't run
)
let promise = new Promise(function(resolve, reject) {
setTimeout(() => reject(new Error("Whoops!")), 1000)
})
// reject runs the second function in .then
promise.then(
result => console.log(result), // doesn't run
error => console.log(error) // shows "Error: Whoops!" after 1 second
)