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. Fixing errors becomes easier as a debugging tool or error console will tell you which file contains the error and reliably report the line number.You can easily find your script if you need to modify it, avoiding the need to scan through long HTML documents to find the place to fix a problem.The next time this user loads the same script it will not be taken from your server but from their own computers - thus loading much faster. Caching means that browsers will take a copy of your JavaScript and store it on the computer of the visitors surfing on your site. Your JavaScript will be cached by browsers.You can apply the same JavaScript functionality to several HTML documents and still keep maintenance easy: if there is a desired change in functionality all you need to do is change one single file.
Keeping your code in an external JavaScript file makes a lot of sense: Īlert( 'I am pointless as I will not be executed') The following example will load the file myscript.js and execute the code in it, but will not execute the alert inside the script element at all. Any content inside the script element itself will be skipped when you provide a src attribute. Upon meeting this element in a page, browsers will then load the file myscript.js and execute it. 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: However, for strict XHTML documents, it is much more sensible not to embed any JavaScript but instead keep it in an external document. However, if you are using strict XHTML as your DOCTYPE, you need to enclose any JavaScript in a CDATA block to make it validate (do not worry about why - it is not really important at this stage in your learning): As this only applies to very old browsers you do not need to bother with that any longer. In the past there was a need to comment out JavaScript with an HTML comment to prevent browsers from showing the code as HTML. VBScript usage died however, as it only works in IE.
This is a throwback to the bad old days, when VBScript was also in popular use on web pages. This is not part of any standard and is utterly useless delete this where you can. Note: You will find script examples on the web that have a language="javascript" attribute. 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.Īs 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: var x = 3 The most basic inclusion of JavaScript inside your HTML page would look something like this: var x = 3 Īlert( 'hello there, I am JavaScript - x is ' + x)
Including your JavaScript inside your HTML document To run JavaScript in console environment, please check out Mozilla Rhino to run JavaScript in server environment, please check node.js.
JavaScript does not have to stay inside browsers. We will look at both of these methods inside this section. js extension) and then reference that file inside the HTML document using an empty script element with a src attribute. To execute JavaScript in a browser you have two options - either put it inside a script element anywhere inside an HTML document, or put it inside an external JavaScript file (with a.
Other languages like Java and C++ need to be compiled to be executable but JavaScript is executed instantly by a type of program that interprets the code called a parser (pretty much all web browsers contain a JavaScript parser). JavaScript is a text-based language that does not need any conversion before being executed. What is JavaScript and how do you execute it? In this article of the Web Standards Curriculum, we will cover the basics of JavaScript - how and where to use it, what problems to avoid, and general basics to get you started on your journey towards becoming a top-notch JavaScript developer. This article provides a basic introduction to coding with JavaScript.