JavaScript can be inserted into an HTML document by including
external JavaScript files or writing page-level inline JavaScript, which
is basically the contents of an external JavaScript file literally
embedded in the HTML page as a text node. Don’t confuse element inline JavaScript contained in
attribute event handlers (i.e., <div onclick="alert('yo')"></div>)
with page inline JavaScript (i.e.,
<script>alert('hi')</script>).
Both methods of inserting JavaScript into an HTML document require
the use of a <script> element node. The
<script> element can contain JavaScript code or
can be used to link to external JavaScript files via the
src attribute. Both methods are explored in the
following code example.
<!DOCTYPE html> <html lang="en"> <body> <!-- external, cross domain JavaScript include --> <script src="http://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.3.3/underscore-min.js"></script> <!-- page inline JavaScript --> <script> console.log('hi'); </script> </body> </html>
It’s possible to insert and execute JavaScript in the DOM by
placing the JavaScript in an element attribute event handler (i.e.,
<div onclick="alert('yo')"></div>) and
using the javascript: protocol (e.g., <a
href="javascript:alert('yo')"></a>), but this is no
longer considered a modern practice.
Trying to include an external JavaScript file and writing page
inline JavaScript using the same <script> element will result ...
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