How can I hide or encrypt JavaScript code?

You can obfuscate it, but there's no way of protecting it completely.

example obfuscator: https://obfuscator.io

While everyone will generally agree that Javascript encryption is a bad idea, there are a few small use cases where slowing down the attack is better than nothing. You can start with YUI Compressor (as @Ben Alpert) said, or JSMin, Uglify, or many more.

However, the main case in which I want to really 'hide stuff' is when I'm publishing an email address. Note, there is the problem of Chrome when you click on 'inspect element'. It will show your original code: every time. This is why obfuscation is generally regarded as being a better way to go.

On that note, I take a two pronged attack, purely to slow down spam bots. I Obfuscate/minify the js and then run it again through an encoder (again, this second step is completely pointless in chrome).

While not exactly a pure Javascript encoder, the best html encoder I have found is http://hivelogic.com/enkoder/. It will turn this:

<script type="text/javascript">
//<![CDATA[
<!--
var c=function(e) { var m="mail" + "to:webmaster";var a="somedomain"; e.href = m+"@"+a+".com";  
};
//-->
//]]>
</script>
<a href="#" onclick="return c(this);"><img src="images/email.png" /></a>

into this:

<script type="text/javascript">
//<![CDATA[
<!--
var x="function f(x){var i,o=\"\",ol=x.length,l=ol;while(x.charCodeAt(l/13)!" +
"=50){try{x+=x;l+=l;}catch(e){}}for(i=l-1;i>=0;i--){o+=x.charAt(i);}return o" +
".substr(0,ol);}f(\")87,\\\"meozp?410\\\\=220\\\\s-dvwggd130\\\\#-2o,V_PY420" +
"\\\\I\\\\\\\\_V[\\\\\\\\620\\\\o710\\\\RB\\\\\\\\610\\\\JAB620\\\\720\\\\n\\"+
"\\{530\\\\410\\\\WJJU010\\\\|>snnn|j5J(771\\\\p{}saa-.W)+T:``vk\\\"\\\\`<02" +
"0\\\\!610\\\\'Dr\\\\010\\\\630\\\\400\\\\620\\\\700\\\\\\\\\\\\N730\\\\,530" +
"\\\\2S16EF600\\\\;420\\\\9ZNONO1200\\\\/000\\\\`'7400\\\\%n\\\\!010\\\\hpr\\"+
"\\= -cn720\\\\a(ce230\\\\500\\\\f730\\\\i,`200\\\\630\\\\[YIR720\\\\]720\\\\"+
"r\\\\720\\\\h][P]@JHADY310\\\\t230\\\\G500\\\\VBT230\\\\200\\\\Clxhh{tzra/{" +
"g0M0$./Pgche%Z8i#p`v^600\\\\\\\\\\\\R730\\\\Q620\\\\030\\\\730\\\\100\\\\72" +
"0\\\\530\\\\700\\\\720\\\\M410\\\\N730\\\\r\\\\530\\\\400\\\\4420\\\\8OM771" +
"\\\\`4400\\\\$010\\\\t\\\\120\\\\230\\\\r\\\\610\\\\310\\\\530\\\\e~o120\\\\"+
"RfJjn\\\\020\\\\lZ\\\\\\\\CZEWCV771\\\\v5lnqf2R1ox771\\\\p\\\"\\\\tr\\\\220" +
"\\\\310\\\\420\\\\600\\\\OSG300\\\\700\\\\410\\\\320\\\\410\\\\120\\\\620\\" +
"\\q)5<: 0>+\\\"(f};o nruter};))++y(^)i(tAedoCrahc.x(edoCrahCmorf.gnirtS=+o;" +
"721=%y;++y)87<i(fi{)++i;l<i;0=i(rof;htgnel.x=l,\\\"\\\"=o,i rav{)y,x(f noit" +
"cnuf\")"                                                                     ;
while(x=eval(x));
//-->
//]]>
</script>

Maybe it's enough to slow down a few spam bots. I haven't had any spam come through using this (!yet).

No, it's not possible. If it runs on the client browser, it must be downloaded by the client browser. It's pretty trivial to use Fiddler to inspect the HTTP session and get any downloaded js files.

There are tricks you can use. One of the most obvious is to employ a javascript obfuscator.

Then again, obfuscation only prevents casual snooping, and doesnt prevent people from lifting and using your code.

You can try compiled action script in the form of a flash movie.