A few words about the features of JavaScript, in other words, what I knew about this language before I started studying it. First and foremost: JS code is easily integrated into HTML markup and is the de facto standard for Internet browsers. It follows that if you don't know HTML at all, JS will most likely be useless to you. In this opus, I will try to explain everything in as much detail as possible, but we must keep in mind that HTML and JS go side by side, complementing and not replacing each other. For those who have encountered Delphi programming or something similar before, we can, as a first approximation, give the following analogy: HTML is a form, and JS is the program code itself. Another important feature of the language is high interactivity. I will quote a phrase that I have heard many times: “JavaScript is an event-driven programming language.” What does it mean? This means that you can write a piece of code that will be executed when the user clicks on a button, you can write a piece of code that will be executed when you move the mouse cursor over it. For Java Script, both are events and it can react to them. A distinctive feature of the language and the code on it is that the result can be seen with only one of the modern browsers. That is, you do not need to install and configure any compilers, programming environments, and so on. To run any of the examples below, just type the text in any editor (notepad, for example), change the extension to html and open it using a browser. That's it.