Including JavaScript Code
JavaScript code could be included two ways:
either embedded into an HTML page, or in an external file.
embedded
<script type="text/javascript">
window.alert("Welcome to JavaScript!");
</script>
You can place this <script> element anywhere, and the code is will be executed after this part of the HTML page has been loaded .
External JavaScript Files
Relative URL :<script language="JavaScript" type="text/javascript" src="jquery.js"></script>
Absolute URL :
<script language="JavaScript" type="text/javascript" src="http://hostname/jquery.js"> </script>
Absolute URL :
<script language="JavaScript" type="text/javascript" src="http://hostname/jquery.js"> </script>
The external file contains only the JavaScript code, no <script> elements . however, A <script> element is used to load the external file .
The src attribute holds the URL of the external script , and could be relative or absolute URLs .
Dynamically Loading JavaScript Files
Sometimes it is necessary to load JavaScript code on demand, while a site is running. For instance, depending on user input, a specific external JavaScript file must be loaded.
One attempt is to use document.write() to dynamically add a new <script> element to the page. However, this fails with some browsers and also is not considered good style.
A better solution is to use DOM. First, you create a new <script> element and set the appropriate attributes. Then, you add this element to the page's DOM . Usually, the code is put in the <head> section of the page. The following shows the complete code; note that there actually is a <head> element so that the code works.
<script language="JavaScript" type="text/javascript">
var e = document.createElement("script");
e.setAttribute("type", "text/javascript");
e.setAttribute("language", "JavaScript");
e.setAttribute("src", "jquery.js");
document.getElementsByTagName("head")[0].appendChild(e);
</script>
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