A Promise is an object that represents either completion or failure of a user task. A promise in JavaScript can be in three states pending, fulfilled, or rejected.
The main advantage of using a Promise in JavaScript is that a user can assign callback functions to the promises in case of a rejection or fulfillment of a Promise, also by using promises one can easily handle the control flow of all the Asynchronous events or data upcoming. As the name suggests a promise is either kept or broken. So, a promise is either completed(kept) or rejected(broken).
Promise resolve() method: The promise.resolve() method in JS returns a Promise object that is resolved with a given value. Any of the three things can happen:
- If the value is a promise then the promise is returned.
- If the value has a “then” attached to the promise, then the returned promise will follow that “then” to till the final state.
- The promise fulfilled with its value will be returned.
Syntax:
Promise.resolve(value);
Parameters: Value(s) to be resolved by this Promise.
Return Value: Either the promise of the promise fulfilled with its value is returned.
Example 1: In this example, we will see a basic example of a promise. resolve method.
javascript
let promise = Promise.resolve(17468);
promise.then(function (val) {
console.log(val);
});
|
Output:
17468
The above example is made using the old version approach we may also use the newest arrow function-based approach and also try to avoid writing var datatype since it may mix up several other variables and may produce incorrect results. Below is the shortest approach for the above-stated approach.
Example: Following is the code snippet that shows the other version of the above-illustrated approach-
Javascript
Promise.resolve(17468).then((value) => console.log(value));
|
Output:
17468
Resolving an array: Here in the below example, we will be using a timer function called setTimeout() will be responsible for the execution of the values which are passed inside resolve() which is passed inside that timer function.
javascript
const promise = new Promise((resolve, reject) => {
setTimeout(() => {
resolve([89, 45, 323]);
}, 5000);
});
promise.then(values => {
console.log(values[1]);
});
|
Output:
45
Resolving another Promise: In the below example, we will be resolving the first promise inside another newly created promise in which we have defined one timer function (setTimeout).
javascript
const promise = Promise.resolve(3126);
const promise1 = new Promise((resolve, reject) => {
setTimeout(() => {
promise.then(val => console.log(val));
}, 5000);
});
promise1.then(vals => {
console.log(vals);
});
|
Output:
3126
We have a complete list of Javascript Promise methods, to check those please go through the Javascript Promise Complete Reference article.
Supported Browsers:
- Google Chrome 32 and above
- Mozilla Firefox 29 and above
- Opera 19 and above
- Safari 8 and above
- Edge 12 and above
- Internet Explorer not supported
JavaScript is best known for web page development but it is also used in a variety of non-browser environments. You can learn JavaScript from the ground up by following this JavaScript Tutorial and JavaScript Examples.