Terry  Tremblay

Terry Tremblay

1602158520

A Gentle Introduction to JavaScript Promises. I Promise :).

Asynchronous operations before promises.

Sometimes you have a function or operation that takes a considerable amount of time to finish like a network/service request to fetch some data or resource but then you want to continue executing the rest of your program and then use the data returned from the operation whenever the process completes.

Instead of waiting on the call to complete you can let the rest of your program that doesn’t rely on the data from the operation to continue running and only run the dependent code after the operation returns a value.

Promises are a fairly new API in JavaScript so we will first look at how asynchronous operations were done before promises. The most common way was to pass in callback functions that were called and ran after the success or failure of the asynchronous function.

We will use a simple social media application page where a user’s basic information and list of their friends are displayed as an example. To get all the data needed to display the page we might need to call multiple services but we might not be able to call all of them simultaneously as some calls will likely depend on data from another service.

In the case of our imaginary social media app we might need to call the login service first and then call the user information service once the user’s credentials are validated. If the login is successful then we might want to use the user’s id to fetch their friends list to display on the page along with other data.

Here is some code we might use to get the data we need to render the page. Some code has been omitted for brevity.

function successCallback(userData) {
    // display user's basic information and a list of their friends        // if the operation completed successfully
}

function errorCallback(errorMessage) {
    // display the error message.
}
function login(successCallback, errorCallback, userName, password) {
    // do some operation here then run the callback function
    // call the user service
    callUserInfoService(userName, password, function(user, error) {
        if(user) {
            // get the user's friends
             getUserFriends(user, function(friends, error) {
                 // call the friends service
                 if(friends) {
                     successCallback({
                         friends : friends
                     });
                 } else {
                      errorCallback(error);
                 }
            });
        } else {
            errorCallback(error);
        }
    });
}
login(successCallback, errorCallback, userName, password);

#software-engineering #software-development #javascript #javascript-tips #promises

What is GEEK

Buddha Community

A Gentle Introduction to JavaScript Promises. I Promise :).
Terry  Tremblay

Terry Tremblay

1602158520

A Gentle Introduction to JavaScript Promises. I Promise :).

Asynchronous operations before promises.

Sometimes you have a function or operation that takes a considerable amount of time to finish like a network/service request to fetch some data or resource but then you want to continue executing the rest of your program and then use the data returned from the operation whenever the process completes.

Instead of waiting on the call to complete you can let the rest of your program that doesn’t rely on the data from the operation to continue running and only run the dependent code after the operation returns a value.

Promises are a fairly new API in JavaScript so we will first look at how asynchronous operations were done before promises. The most common way was to pass in callback functions that were called and ran after the success or failure of the asynchronous function.

We will use a simple social media application page where a user’s basic information and list of their friends are displayed as an example. To get all the data needed to display the page we might need to call multiple services but we might not be able to call all of them simultaneously as some calls will likely depend on data from another service.

In the case of our imaginary social media app we might need to call the login service first and then call the user information service once the user’s credentials are validated. If the login is successful then we might want to use the user’s id to fetch their friends list to display on the page along with other data.

Here is some code we might use to get the data we need to render the page. Some code has been omitted for brevity.

function successCallback(userData) {
    // display user's basic information and a list of their friends        // if the operation completed successfully
}

function errorCallback(errorMessage) {
    // display the error message.
}
function login(successCallback, errorCallback, userName, password) {
    // do some operation here then run the callback function
    // call the user service
    callUserInfoService(userName, password, function(user, error) {
        if(user) {
            // get the user's friends
             getUserFriends(user, function(friends, error) {
                 // call the friends service
                 if(friends) {
                     successCallback({
                         friends : friends
                     });
                 } else {
                      errorCallback(error);
                 }
            });
        } else {
            errorCallback(error);
        }
    });
}
login(successCallback, errorCallback, userName, password);

#software-engineering #software-development #javascript #javascript-tips #promises

Julie  Donnelly

Julie Donnelly

1602406920

JavaScript Promise: Methods Comparison

Introduction

Promises in JavaScript are used to handle asynchronous operations by keeping track of whether a certain event has happened. If that certain event has taken place, it determines what happens next. Promises return a value which is either a resolved value or a reason why it’s rejected. They can handle multiple asynchronous operations easily and they provide better error handling than callbacks and events.

Callback: A callback is a function that is passed into another function as an argument to be executed later.

Events: Events provide a dynamic interface to a WebPage and are connected to elements in the Document Object Model(DOM), for example: onclick(), onmouseover() etc.

A Promise has four states

Pending: Before the event has happened, the promise is in the pending state.

Settled: Once the event has happened it is then in the settled state.

Fulfilled: Action related to the promise has succeeded.

Rejected: Action related to the promise has failed.

#javascript #javascript-development #javascript-tutorial #promises #javascript-tips

Introduction With Basic JavaScript

The world’s most misunderstood programming language is JavaScript but JavaScript is now used by an incredible number of high-profile applications. So, it’s an important skill for any web or mobile developer to enrich the deeper knowledge in it.

Unlike most programming languages, the JavaScript language has no concept of input or output. It is designed to run as a scripting language in a host environment, and it is up to the host environment to provide mechanisms for communicating with the outside world.

Its syntax is based on the Java and C languages — many structures from those languages apply to JavaScript as well. JavaScript supports object-oriented programming with object prototypes, instead of classes. JavaScript also supports functional programming — because they are objects, functions may be stored in variables and passed around like any other object.

Let’s start off by looking at the building blocks of any language: the types. JavaScript programs manipulate values, and those values all belong to a type. JavaScript’s types are:

· Number

· String

· Boolean

· Function

· Object

· Symbol

and undefined and null, which are … slightly odd. And Array, which is a special kind of object. Date and RegExp, which are objects that you get for free. And to be technically accurate, functions are just a special type of object. So the type of diagram looks like this:

#beginner-javascript #javascript #javascript-introduction #javascript-fundamental #basic-javascritp

Promise.allSettled() vs Promise.all()

Promise.allSetlled() is recently introduced in ECMA 2020.
Check out how it is different from Promise.all()

https://www.geekstutorialpoint.com/2020/05/promiseallsettled-vs-promiseall.html

#javascript #promise.all #promise.allsettled #ecma #promise #jquery

Rahul Jangid

1622207074

What is JavaScript - Stackfindover - Blog

Who invented JavaScript, how it works, as we have given information about Programming language in our previous article ( What is PHP ), but today we will talk about what is JavaScript, why JavaScript is used The Answers to all such questions and much other information about JavaScript, you are going to get here today. Hope this information will work for you.

Who invented JavaScript?

JavaScript language was invented by Brendan Eich in 1995. JavaScript is inspired by Java Programming Language. The first name of JavaScript was Mocha which was named by Marc Andreessen, Marc Andreessen is the founder of Netscape and in the same year Mocha was renamed LiveScript, and later in December 1995, it was renamed JavaScript which is still in trend.

What is JavaScript?

JavaScript is a client-side scripting language used with HTML (Hypertext Markup Language). JavaScript is an Interpreted / Oriented language called JS in programming language JavaScript code can be run on any normal web browser. To run the code of JavaScript, we have to enable JavaScript of Web Browser. But some web browsers already have JavaScript enabled.

Today almost all websites are using it as web technology, mind is that there is maximum scope in JavaScript in the coming time, so if you want to become a programmer, then you can be very beneficial to learn JavaScript.

JavaScript Hello World Program

In JavaScript, ‘document.write‘ is used to represent a string on a browser.

<script type="text/javascript">
	document.write("Hello World!");
</script>

How to comment JavaScript code?

  • For single line comment in JavaScript we have to use // (double slashes)
  • For multiple line comments we have to use / * – – * /
<script type="text/javascript">

//single line comment

/* document.write("Hello"); */

</script>

Advantages and Disadvantages of JavaScript

#javascript #javascript code #javascript hello world #what is javascript #who invented javascript