We will look at both of these methods inside this section. JavaScript does not have to stay inside browsers. To run JavaScript in console environment, please check out Mozilla Rhino ; to run JavaScript in server environment, please check node. You could put this anywhere inside your document and it would execute, but some places are definitely better than others — see the Where to put JavaScript section for guidance on this.
As there might be several different types of script available to use on web pages in the future, it makes sense to add the name of the script you are using as a MIME type:. This is not part of any standard and is utterly useless; delete this where you can.
This is a throwback to the bad old days, when VBScript was also in popular use on web pages. VBScript usage died however, as it only works in IE. As this only applies to very old browsers you do not need to bother with that any longer. In order to link to an external JavaScript either on the same server or anywhere on the internet all you have to do is to add a src attribute to your script element:.
Upon meeting this element in a page, browsers will then load the file myscript. Any content inside the script element itself will be skipped when you provide a src attribute.
The following example will load the file myscript. You can add as many JavaScript files as you want to a document, but there are several considerations to make before going down that route. Cutting up a lot of JavaScript into different files, each dealing with one task at a time, is a great idea to keep your functionality easy to maintain and allow for quick bug-fixing.
For example, you could have several script blocks like these:. However, the development benefits of this are diminished by the effect this has on the performance of your document. This differs slightly from browser to browser but the worst-case scenario which is sadly enough still the second most-used browser does the following:. All of this means that the display of your web site is slowed down until all of these steps happen for all the scripts you include.
This can become annoying for your visitors. One way around this is to use a backend script to create a single file from all the files you use. That way you have the benefit of keeping maintenance easy while simultaneously cutting down on delays to your web page display.
You can and often will attach multiple external JavaScript files to a single web page. For example, you might have created one external JavaScript file that controls a drop-down navigation panel, and another that lets you add a nifty slideshow to a page of photos. In addition, you can attach external JavaScript files and add a JavaScript program to the same page like this:.
The home page top includes a row of navigation buttons along the top—Men, Women, Kids, and so on—that, when moused over, reveal a panel of additional navigation options.
For example, mousing over the Sports button circled in bottom image reveals a panel listing different sports that Nike makes products for. There are three types of paths: absolute path, root-relative path , and document-relative path. All three indicate where a web browser can find a particular file. An absolute path is like a postal address—it contains all the information needed for a web browser located anywhere in the world to find the file. A document-relative path specifies the path from the web page to the JavaScript file.
For example, suppose you have a JavaScript file named site. Root-relative paths are good for JavaScript files stored on your own site.
Because they always start at the root folder, the URL for a JavaScript file will be the same for every page on your website, even when web pages are located in folders and subfolders on your site. You can create an external JavaScript file, attach it to a web page, and then check the JavaScript in a web browser simply by opening the web page off your hard drive.
This book uses document-relative paths, which will let you follow along and test the tutorials on your own computer without a web server. Sometimes the order in which you attach external JavaScript files matters. The best way to learn JavaScript programming is by actually programming. The tutorial files are stored as a single Zip file. In Windows, download the Zip file and double-click it to open the archive. Click the Extract All Files option, and then follow the instructions of the Extraction Wizard to unzip the files and place them on your computer.
If you have trouble opening the Zip file, the free 7-Zip utility can help: www. On a Mac, simply double-click the file to decompress it. To get your feet wet and provide a gentle introduction to JavaScript, your first program will be very simple:. In your favorite text editor, open the file hello. It informs the web browser that the stuff following this tag is JavaScript. Press the Return key to create a new blank line, and type :.
The JavaScript alert function is a command that pops open an Alert box and displays the message that appears inside the parentheses—in this case, hello world. The code should now look like this :. In this example, the stuff you just typed is shown in boldface.
The two HTML tags are already in the file; make sure you type the code exactly where shown. Launch a web browser and open the hello. A JavaScript Alert box appears see Figure Notice that the page is blank when the alert appears. Double-check your typing and read the following Tip. For new programmers, the most common cause of nonfunctioning programs is simple typing mistakes. Always double-check to make sure you spelled commands like alert in the first script correctly.
Also, notice that punctuation frequently comes in pairs the opening and closing parentheses, and single-quote marks from your first script, for example. So when you try to preview the tutorial files for this book in Internet Explorer, you might see a message saying that IE has blocked the script. This annoying behavior only applies to web pages you preview from your computer, not to files you put up on a web server.
The script in the previous section popped up a dialog box in the middle of your monitor. What if you want to print a message directly onto a web page using JavaScript? In your text editor, open the file hello2. Like the alert function, document. The tutorial files you downloaded also include the completed version of each tutorial.
The two scripts you just created may leave you feeling a little underwhelmed with JavaScript…or this book. You then instruct your web pages to load that file and use the JavaScript inside it. In particular, there are collections of JavaScript code called libraries , which provide useful JavaScript programming. This is the way to include an external javascript file to you HTML markup.
Xmindz Xmindz 1, 13 13 silver badges 33 33 bronze badges. Even though it works, it's not recommended to put Javascript in href. Just write the code and enjoy! Clomp 2, 1 1 gold badge 19 19 silver badges 35 35 bronze badges. Welcome to StackOverflow. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. Podcast Making Agile work for data science.
Stack Gives Back If we enclose that inside HTML script tags, it will look like this:. If we place the above JavaScript between the head tags or body tags , it will run as soon as we load the page.
But, what if you don't want it to run as soon as the page loads? What if you only want it to run when a user clicks on a button? Event handlers allow your web page to detect when a given "event" has occurred, so that it can run some JavaScript code.
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