Skip to main content

Promise vs Observable difference


Promise vs Observable difference

Promise

  1. It resolves or reject a single value and can handle a single value async task at a time.
  2. A promise once resolved the async value it completes, can no longer be used.its just one-time use and here it falls short.
  3. Not cancellable
  4. No rxjs support for operators. 
    read more about promise



Observable

  1. ability to emit multiple asynchronous values.
  2. Used to handle the stream of events or values. Consider you have an array of numerous tasks or values, and you want every time value is inserted into this it should be handled automatically. Anytime you push a value into this array, all of its subscribers will receive the latest value automatically.
  3. Observables are useful for observing input changes, repeated interval, broadcast values to all child components, web socket push notifications etc.
  4. Can be canceled using the unsubscribe method anytime.
  5. One more last good part that promise that has is support for rxjs operators. You have many pipe operators majorly map, filter, switchMap, combine latest etc. to transform observable data before subscribing.

operation      observables Promise
creation
const obs= new Observable((observer) => {
    observer.next(5);
});

const promise= new Promise((resolve) => {
    resolve(5);
});
Subscribe
const sub= obs.subscribe(value => console.log(value));
promise.then(value => console.log(value));
unsubscribe
sub.unsubscribe();

   no cancellable

Comments

Popular

JavaScript type hoisting with variable function Expression

JavaScript type hoisting with variable function Expression Hoisting is JavaScript default behavior to moving declaration on the top. Variable can be used before its declaration. To understand this, first we need to understand of hoist meaning, hoist means “raise(something) by means of ropes & pulleys”. now we can relate hoisting with JavaScript. JavaScript interpreter moves all declaration on the top at runtime. It is best practice to declare all variable at the top of their respective scopes. , JavaScript is loosely syntax language so it will not throw any error at runtime if the variable used before its declaration. But JavaScript does not allow variable used before its declaration in “use strict” mode. Example 1 In this example, we can see in a normal scenario, when y has declared & then used. in this case, it will give output 10 as excepted. <p id= "demo" ></p> <script> var y; //Declare y y = 10 ; ...

Building Block of Angular

The main building blocks for Angular are modules, components, templates, metadata, data binding, directives, services, and dependency injection. Below mentioned are the main building blocks of an Angular application: - Modules  group components logically within the project. Angular basically is a modular framework where every block of functionality is encapsulated within a module and exposed outside within the project as a service. There are two types of modules one is encapsulating block of function within a single component and the other is encapsulating block of function within single or group of components by providing exposure in a unified manner via an interface. Components  help in controlling UI block and also it provides data and logic. It represents a unique "View" and "View Model" in MVVM pattern or exactly like what Controllers do in Angular 1. The "V...

HTML Basic

HTML (Hypertext Markup Language) Basic What is HTML ? HTML invented by Tim Berners-Lee in 1990. HTML stands for hypertext markup language. Web browsers receive HTML documents from a web server or from local storage and render the documents into multimedia web pages .We can create web page with different elements like audio, video, image, tables, link, list & text etc, with CSS & JavaScript. version of HTML There are 6 version of HTML HTML Version Year HTML 1991 HTML 2.0 1995 HTML 3.2 1997 HTML 4.01 1999 XHTML 2000 HTML 5 2014 (Latest version) Latest version of HTML Latest version of html is HTML 5.0 , in latest version of html provided new tags for multimedia support. Now we are creating web page  index.html  How we can create Web page <!DOCTYPE html> < html > < head > < title > This is my First Web Page </ title > </ head > < body > < h1 > My First heading ...