AsciiDoc supports syntax highlighting of code in PDFs when you use the dblatex backend (the default).

a2x -f pdf yourdoc.asciidoc

However, dblatex does not include support for JavaScript (rather suprisingly). Thus, the following snippet in your document will cause pdf generation to fail:

[source,javascript]
----
function add(a, b) {
    return a + b;
}

int total = add(2, 2);
----

In order to make this work, you need to define a new language in a custom dblatex style configuration file (extension .sty). AsciiDoc already uses a custom file, and dblatex only supports a single configuration file, so you first need to copy the file into your build directory (or wherever you want to stick it).

cp %ASCIIDOC_INSTALL_DIR%/dblatex/asciidoc-dblatex.sty custom-asciidoc-dblatex.sty

Next, append the following code to that custom file:

\usepackage[usenames,dvipsnames]{xcolor}

% Set custom colors
\definecolor{code}{gray}{0}
\definecolor{canvas}{gray}{0.96}
\definecolor{comment}{rgb}{0, 0.456, 0}
\definecolor{keyword}{rgb}{0.5, 0, 0.5}

% JavaScript is not part of the listings package...
% but thankfully this page shows how to add it:
% http://lenaherrmann.net/2010/05/20/javascript-syntax-highlighting-in-the-latex-listings-package

\lstdefinelanguage{javascript}{
  keywords={typeof, new, true, false, catch, function, return, null, catch, switch, var, if, for, in, while, do, else, case, break},
  ndkeywords={class, export, boolean, throw, implements, import, this},
  sensitive=false,
  comment=[l]{//},
  morecomment=[s][\color{blue}\ttfamily]{/*}{*/},
  morestring=[b]',
  morestring=[b]"
}

% Parameters for formatting code (optional, affects all code listings)
\lstset{
  backgroundcolor=\color{canvas},
  basicstyle=\ttfamily\small\color{code},
  commentstyle=\color{comment},
  identifierstyle=\color{black},
  keywordstyle=\color{keyword}\bfseries,
  ndkeywordstyle=\color{keyword}\bfseries,
  stringstyle=\color{blue}\ttfamily
}

Finally, you need to pass this style configuration to the a2x command via the dblatex-opts flag:

a2x -f pdf --dblatex-opts="-s custom-asciidoc-dblatex.sty" yourdoc.asciidoc

Now you should see the JavaScript code highlighted in the generated pdf.

This tip builds on the following blog post on this topic: http://lenaherrmann.net/2010/05/20/javascript-syntax-highlighting-in-the-latex-listings-package