Reading blog 2 | bhavyajoshi

Why JavaScript

JavaScript (JS) fulfilled a great need for websites to be dynamic, and interactive. In fact JS is so interactive that you can play complex games in the browser all coded in it. JS is a dynamic programming language that was invented by Brendan Eich of the Mozilla Foundation in 1995. Did you know that JS is managed by committees that consist of several companies which are actually rivals but work together to help improve the language? Imagine being that powerful! A few of the main features of JS are:

It is part of the web platform i.e HTML5 thus it enables you to build powerful applications
It is both functional and object oriented, and is one of the few languages that follow both programming paradigms
It is dynamic in nature and dynamically typed i.e. variable and object properties can hold values of any type

JavaScript Basics

Adding to HTML5: JS can be added to HTML5 in multiple ways:
1. By adding the
```
<script> </script>
```
  tag inside the
```
<head> </head>
```
  of an HTML5 document
2. By adding as inline code inside HTML such as by using "onClick"
3. The best way is to add it as an external JS file by using:
```
<script src="app.js"> </script>
```

Functions in JS: functions in JS are very easy to write as follows:
```
function add(a, b) {
return a + b;
}
```

document.querySelector(): This is probably one of the most important methods in JS. This method allows you to select an HTML element by using either the class (.class) or the id (#id) of the element. You can then add interactivity to your app easily by functions such as addEventListener() as follows:
```
const nextButton = document.querySelector("#next-btn"); 
```
```
nextButton.addEventListener("click", function validateInput() { } 
```

JS Promise: Promises in JS is a concept just like promise in real life, it is an object that promises to produce a certain value in the future when required. Promise in JS is used to handle asynchronous events. It enables a proxy value to be created for a certain value that is required and important in the future. Promise concept allow asynchronous methods to work as if they are synchronous, by working with the proxy value. Promises are in three states:
1. pending: It is the first state where a promise is neither fulfilled nor rejected.
2. fulfilled: It means that the method was successful in completing the operation.
3. rejected: It means that the operation could not be completed successfully, thus the promise has failed
Some important functions used in promises are:
- fetch() : It returns a promise, by informing that execution should be continued instead of waiting for the required data
- .then(): This is the method which is called when promise is resolved i.e. it tells what to do next if a promise is resolved. To execute some tasks, we can use the format
```
userPromise.then( () => {
// task to do
});
```
- .catch(): This method enabled error handling, it is passed if suppose the promise is rejected. This enabled a different response as compared to if the promise was successful. It can written in the following way:
```
userPromise.then( () => {
// task to do on success
}).catch( () => {
//task to do on failure
});
```

We have just brushed over very few important topics in JavaScript. JS is a vast language that requires whole books to really understand it, such as the around 500 pages long "Eloquent JavaScript: A Modern Introduction to Programming"!