What is JavaScript?

JavaScript: definition and distinction

JavaScript emerged in 1995 at the browser maker Netscape and is now the programming language of the web: every common browser can run it. Despite the similar name, it has nothing to do with the Java language. The language standard is called ECMAScript and is developed further every year by the organization Ecma International.

While HTML provides the content and CSS the appearance, JavaScript adds behavior: drop-down menus, form validation, product filters, maps or live search. Web applications in which content changes without a reload are also built on it. Besides the browser, JavaScript now also runs on servers, in apps and in many software development tools.

How JavaScript works

The browser loads the script along with the page and runs it. In doing so, it accesses the page’s elements through the Document Object Model (DOM), responds to events such as clicks and fetches data from the server through interfaces without reloading the page. With the Node.js runtime environment, the same language can also be used for servers, tools and interfaces.

• Frameworks and libraries such as React, Vue or Angular speed up large user interfaces
• Node.js runs JavaScript outside the browser
• npm is the package manager with a huge number of ready-made building blocks
• TypeScript adds types and is compiled to JavaScript

Real-world example: product filters at a specialist retailer

A specialist retailer of plumbing supplies carries several thousand items. With JavaScript, filters for manufacturer, size and price can be built in that update the results instantly instead of loading a new page with every click. Customers find the right part faster and have to browse less.

It is important that the basic functions stay accessible even without scripts, such as navigation and category pages. That way, search engines can reliably read the content, and the page remains usable if a script fails to load or runs slowly on an older device.

Limits, risks and what to watch for

JavaScript lengthens loading time when too much of it is loaded. Third-party scripts such as tracking, chat or advertising in particular slow pages noticeably and hurt metrics such as Interaction to Next Paint (INP). Many tracking scripts may also only be loaded after consent, and unchecked input opens the door to attackers through cross-site scripting.

Nano Concepts develops JavaScript applications, from small interactions to web apps, with a focus on speed, security and data protection. That also includes reviewing existing scripts for legacy code and unnecessary third parties and keeping the page lean. This improves loading time and usability.

• Load only the scripts you need and review third-party scripts regularly
• Validate input and secure output to prevent cross-site scripting
• Do not generate important content exclusively via script
• Load tracking only after consent
• Keep dependencies up to date and check them for known vulnerabilities