# Hello, world! The tutorial that you're reading is about core JavaScript, which is platform-independent. Later on, you'll learn about Node.JS and other platforms that use it. But we need a working environment to run our scripts and, since this book is online, the browser is a good choice. We'll keep the amount of browser-specific commands (like `alert`) to a minimum so that you don't spend time on them if you plan to concentrate on another environment (like Node.JS). We'll focus on JavaScript in the browser in the [next part](/ui) of the tutorial. So first, let's see how we attach a script to a webpage. For server-side environments (like Node.JS), you can execute the script with a command like `"node my.js"`. ## The "script" tag JavaScript programs can be inserted into any part of an HTML document with the help of the ` */!*

...After the script.

``` ```online You can run the example by clicking the "Play" button in the right-top corner of the box above. ``` The ` ``` This trick isn't used in modern JavaScript. These comments hid JavaScript code from old browsers that didn't know how to process the ` ``` Here, `/path/to/script.js` is an absolute path to the script file (from the site root). You can also provide a relative path from the current page. For instance, `src="script.js"` would mean a file `"script.js"` in the current folder. We can give a full URL as well. For instance: ```html ``` To attach several scripts, use multiple tags: ```html … ``` ```smart As a rule, only the simplest scripts are put into HTML. More complex ones reside in separate files. The benefit of a separate file is that the browser will download it and store it in its [cache](https://en.wikipedia.org/wiki/Web_cache). Other pages that reference the same script will take it from the cache instead of downloading it, so the file is actually downloaded only once. That reduces traffic and makes pages faster. ``` ````warn header="If `src` is set, the script content is ignored." A single ` ``` We must choose either an external ` ``` ```` ## Summary - We can use a ``. There is much more to learn about browser scripts and their interaction with the webpage. But let's keep in mind that this part of the tutorial is devoted to the JavaScript language, so we shouldn't distract ourselves with browser-specific implementations of it. We'll be using the browser as a way to run JavaScript, which is very convenient for online reading, but only one of many.