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

Post a Comment

Popular

DOM(Document Object Model) and BOM(Browser Object Model)

DOM(Document Object Model) The DOM is the Document Object Model, which deals with the document, the HTML elements themselves, It organize the elements of the document in tree structure (DOM tree) and in the DOM tree, all elements of the document are defined as objects (tree nodes) which have properties and methods.When a web page is loaded, the browser creates a DOM tree for all the objects (Html elements) of that page. e.g. document and all traversal you would do in it, events, etc. A Simple DOM Tree BOM(Browser Object Model) The BOM is the Browser Object Model, which deals with browser components aside from the document,like history, location, navigator and screen (as well as some others that vary by browser). The Browser Object Model (BOM) in JavaScript includes the properties and methods for JavaScript to interact with the web browser. BOM provides you with window object, for example, to show the width and height of the window. It also includes the window.scre...
Post a Comment
Read more

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 ; ...
4 comments
Read more

AOT compilation

What is AOT compilation What are the advantages of AOT Every Angular application consists of components and templates which the browser cannot understand. Therefore, all the Angular applications need to be compiled first before running inside the browser.  Angular provides two types of compilation:  JIT(Just-in-Time) compilation AOT(Ahead-of-Time) compilation In JIT compilation, the application compiles inside the browser during runtime.  Whereas in the AOT compilation, the application compiles during the build time.  The advantages of using AOT compilation are:  Since the application compiles before running inside the browser, the browser loads the executable code and renders the application immediately, which leads to  faster rendering . In AOT compilation, the compiler sends the external HTML and CSS files along with the application, eliminating separate AJAX requests for those source files, which leads to  fewer ajax requests . Developers can detec...
Post a Comment
Read more