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GeezerVison is showing github.com — JavaScript/Asynchronous-JavaScript/Promises.js at master · lgope/JavaScript

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// From Callback Hell to Promises (ES6)
/* Promises, which is an ES six feature designed specifically
to deal with asynchronous JavaScript. In simple terms a promise is an object
that keeps track about whether a certain event
has happened already or not, and if it did happen,
then the promise determines what happens next. A promise kind of implements the concept
of a future value that we're expecting.*/
const getIDs = new Promise((resolve, reject) => {
setTimeout(() => {
resolve([523, 883, 432, 974]);
}, 1500);
});
const getRecipe = recID => {
return new Promise((resolve, reject) => {
setTimeout(ID => {
const recipe = {
title: 'Fresh tomato Pasta',
Publisher: 'Lakshman'
};
resolve(`${ID}: ${recipe.title}`);
}, 1500, recID);
});
};
const getRelated = Publisher => {
return new Promise((resolve, reject) => {
setTimeout(pub => {
const recipe = {
title: 'American Pizza',
Publisher: pub
};
resolve(`${pub}: ${recipe.title}`); // 3
}, 1500, Publisher);
});
};
// this then method allows us to add an event handler for the case that the promise is fulfilled. So which means that there is a result.
getIDs
.then(IDs => { // so this argument here will be the result of the successful promise.
console.log(IDs); // [ 523, 883, 432, 974 ]
return getRecipe(IDs[2]);
})
.then(recipe => {
console.log(recipe); // 432: Fresh tomato Pasta
return getRelated('Lakshman Gope');
})
.then(recipe => {
console.log(recipe); // Lakshman Gope: American Pizza
})
// if the promise rejected then catch method will catch the error.
.catch(error => {
console.log('Error: ' + error);
});
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