Promises in javascript is an important concept that is essential for a javascript developer to understand. If this concept is clear, the developer can utilize this in a variety of ways in their day-to-day lives.
There are lot of articles, tutorials available on the web about promises. But, very few of them act as a comprehensive guide to make use of promises. In this article, I will try to elaborate promises in depth. So you won't need to go through other resources.
Getting To Know More About The Promise Object
var isPossibleToPurchaseGift = true;
var giftPromise = new Promise(function(resolve, reject) {
if(isPossibleToPurchaseGift) {
resolve('You are able to keep your promise');
} else {
reject('You are unable to keep your promise');
}
});
console.log(giftPromise);In the code above, we created a promise, if the value of variable "isPossibleToPurchaseGift" is set to true then the promise is resolved. Finally, we are displaying that promise's resolved state in the browser's console window.
Writing Javascript Promises With ES6/ES2015, ES7
const isPossibleToPurchaseGift = true;
// const isPossibleToPurchaseGift = false;
var willGetNewGift = ()=> {
if(isPossibleToPurchaseGift) {
return Promise.resolve('It is possible to purchase gift');
} else {
const error = new Error('Left my wallet!!');
return Promise.reject(error);
}
};
var willAttendDinner = (purchasedGift)=> {
// purchasedGift = false;
if(purchasedGift) {
return Promise.resolve('It is possible to attend dinner');
} else {
return Promise.reject(new Error('Unable to attend dinner!!'));
}
};
var willGoOnALongDrive = (attendedDinner) => {
// attendedDinner = false;
if(attendedDinner) {
return Promise.resolve('It is possible to go on a long drive');
} else {
return Promise.reject(new Error('Unable to go on a long drive!!'));
}
};
willGetNewGift()
.then(willAttendDinner)
.then(willGoOnALongDrive)
.then(response =>console.log(response))
.catch(error =>console.log(error.message));Again, to understand the code better I would advise you to uncomment commented codes one at a time. This way you will understand better.
Conclusion
I hope after reading this article you will understand javascript promises in depth. If you find this article as helpful, don't forget to share it among others. Thank you!