How do I write a JavaScript?

Updated: 12/31/2017 by Computer Hope
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To write a JavaScript, you need a web browser and either a text editor or an HTML editor.

Once you have the software in place, you can begin writing JavaScript code. To add JavaScript code to an HTML document, you need to create or open an HTML file with your text/HTML editor. A basic HTML file has a docType and some basic HTML tags such as <html>, <head> and <body>. For example, a basic HTML 5 document might look something like what is shown below.

<title>Testing JavaScript</title>
[Content goes here]

When you see JavaScript code on the Web, you will sometimes see some JavaScript code between the <head></head> tags. Or, you may see it in the <body></body> tags (or even in both places). To separate JavaScript code from HTML code, you need to enclose it within a set of <script></script> tags. The opening <script> tag has one required attribute and one optional attribute. The required attribute is the type attribute, while the optional attribute is src (which allows you to point to an external script file, covered later in this answer). The value of the type attribute is set to text/javascript, as shown below.

<script type="text/javascript">
Your JavaScript code goes here.

As you can see, your JavaScript code is placed between the opening and closing script tags. As an example script, you could write a simple string of text directly on the web page, as shown in the code below (place this between the <body> and </body> tags):

<script type="text/javascript">
document.write("Text written using JavaScript code!");

In the above example, the standard JavaScript function to displays text between the quotation marks on the page. It would look like the example below.

Another option for including a JavaScript on a page is to create the script in an external text file and save it with a .js extension (making it a JavaScript file). The .js file is then included in the page using the src attribute of the opening script tag. So, if you wanted to use the script above by placing it in an external file, you would place the JavaScript code (without the script tags) into a new text file, as shown below:

document.write("Text written using JavaScript code!");

You would then save the file with a .js extension. For instance, you could save it as write.js. Once the file is saved, you can call it from the HTML code via the src attribute of the opening script tag, as shown below for write.js.

<script type="text/javascript" src="write.js"></script>

The above procedure has the same effect as writing the code between the script tags, but won't clutter the HTML code with JavaScript code (which can become quite lengthy at times). Another advantage to this method is that the same script can be included in multiple pages, and editing the script file will update the script in every page that uses the external script file. Doing this makes it far easier to edit the script as it can be done in one place (rather than editing the code in the script tags on each page that contains the script).

Now that you know how to add JavaScript code to a web page, you can use any number of JavaScript example scripts or follow a JavaScript tutorial or book to learn more about JavaScript coding.

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