Definition of JavaScript
JavaScript is a scripting language or programming language that allows you to implement complex things on web pages — each time a web page displays more than just static information. - You can bet that JavaScript is probably involved. It is the third layer of layer cake covered by standard web technologies, two of which (HTML and CSS) we have in other parts of the learning area much more detailed.
*HTML is the markup language we use to structure and make sense of our web content, such as defining paragraphs, headings, and data tables, or embedding images and videos into the page.
*CSS is a language of style rules that we use to apply styling to our HTML content, such as setting background colors and fonts, and defining our content in multiple columns.
*JavaScript is a scripting language that allows you to dynamically update content, control multimedia, animate images, and create almost anything else. (Okay, not all, but it's amazing what you can achieve with a few lines of JavaScript code.)

Why JavaScript?
When JavaScript was created, it first had a different name: "LiveScript". But Java was very popular at that time, so it was decided that positioning a new language as a "younger brother" of Java would help.
But as it developed, was JavaScript, a completely independent language with its own specification called ECMAScript, and now It has no relationship at all to Java.




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What does JavaScript do on your page?
Here we start to look at a code and explore what happens when you run JavaScript on your page.
Let's briefly tell the story of what happens when you load a web page into a browser (first in our article how CSS works). When you load a web page in your browser, run your code (HTML, CSS, and JavaScript) in an execution environment (Browser-tab). This is like a factory that takes raw materials (the code) and a product (the site).
The JavaScript is executed by the browser's JavaScript engine after HTML and CSS have been assembled and merged into a web page. This ensures that the structure and style of the page already exists when the JavaScript starts.
This is a good thing, because a very common use of JavaScript is to change the HTML and CSS dynamically to update a user interface via the Document Object Model API (as mentioned above). If the JavaScript loaded and tried to run before the HTML and CSS were there to affect then error would occur.
Browser Security
This means that in most cases the code in each tab is completely separated and the code in one tab cannot directly affect the code in another tab-or on another website. This is a good security measure — if not, Pirates could write code to steal information from other sites, and others such bad things.

What makes JavaScript unique?
There are at least three great things about JavaScript:
Full integration with HTML / CSS.
Simple things are made easy.
Support by all popular browsers and enabled by default.

Javascript is the only browser technology that combines these three things.
This makes JavaScript unique. Therefore, it is the most widely used tool for creating browser interfaces.
While you are planning to learn a new technology, it is beneficial to review your prospects. So let's go to the modern trends that affect it, including new languages and browser capabilities.

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