Understanding Javascript Promise Object

Question

I am trying to wrap my head around promise object in JavaScript. So here I have this little piece of code. I have a promise object and two console.log() on either side of the promise object. I thought it would print

hi

There!

zami

but it printed

hi

zami

There!

Why it is like that? I have zero understanding on how promise works, but I understand how asynchronous callback works in JavaScript. Can any one shed some light on this topic?

console.log('hi');
var myPromise = new Promise(function (resolve, reject) {
    if (true) {
        resolve('There!');
    } else {
        reject('Aww, didn\'t work.');
    }
});

myPromise.then(function (result) {
    // Resolve callback.
    console.log(result); 
}, function (result) {
    // Reject callback.
    console.error(result);
});
console.log('zami');

Accepted Answer

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Summary:

A promise in Javascript is an object which represent the eventual completion or failure of an asynchronous operation. Promises represent a proxy for a value which are getting in some point in the future.

A promise can have 3 states which are the following:

Pending: This is the initial state of the promise, the promise is now waiting for either to be resolved or rejected. For example, when are reaching out to the web with an AJAX request and wrapping the request in a promise. Then the promise will be pending in the time window in which the request is not returned.
Fulfilled: When the operation is completed succesfully, the promise is fulfilled. For example, when we are reaching out to be web using AJAX for some JSON data and wrapping it in a promise. When we are succesfully getting data back the promise is said to be fulfilled.
Rejected: When the operation has failed, the promise is rejected. For example, when we are reaching out to be web using AJAX for some JSON data and wrapping it in a promise. When we are getting a 404 error the promise has been rejected.

Understanding Javascript Promise Object

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Chloe Bennett