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JavaScript is an object-oriented programming language that was first developed in 1995. It’s constantly updated on the basis of the ECMAScript standard, and a new version of the standard has been issued every year since 2015. The contents of this book are based on ECMAScript 2024. The JavaScript language was designed for use in internet browsers. It’s now also used beyond websites, but JavaScript’s use in browsers is the topic of this book. Despite their similarities in individual aspects, JavaScript and Java—another widely used programming language—must be clearly distinguished from each other. JavaScript is an interpreted language, which means JavaScript programs are translated and executed line by line. JavaScript also offers many elements that may be familiar to you from other programming languages, such as loops for a quick repetition of program parts, branches for the different handling of different situations, and functions for breaking down a program into manageable components. You also have a variety of objects at your disposal. Using the Document Object Model (DOM), you can access all elements of your webpages in JavaScript so that you can change them dynamically. The programs are available within internet pages, and they contain JavaScript code along with Hypertext Markup Language (HTML) code. It’s important to note here that JavaScript provides additional possibilities and aids that HTML doesn’t have. After calling up a website with JavaScript code, the code is executed in the browser and can dynamically change the content of the website. This happens either immediately after loading or after the occurrence of an event such as your pressing a button when using the program. JavaScript enables the design of complex applications with a user interface. During development, however, you should make sure that your code doesn’t restrict the use of a website. For example, you should not write a JavaScript program that prevents you from leaving a website, because such a website won’t be visited a second time. Forms play the following important roles in connection with JavaScript:
• They are used to transmit data to a web server. Before sending, the contents of the formats can be checked for validity using JavaScript, which avoids unnecessary network traffic.
• They enable interactions similar to what you’re used to with other computer applications. You can make entries and trigger processing, and the program will return the results.
To simplify the development of your programs, all you need is a text editor that can highlight the HTML markers and JavaScript keywords for clarity. The Notepad++ editor is one of many editors that can do this.