Many websites, like Catch.com, depend on JavaScript heavily. Catch.com for example, when save the webpage, a javascript file: catchapp.js is downloaded, but it's content begins with strange codes, like:
function e(a) { throw a; }
var i = void 0, j = !0, k = null, m = !1;
function ba() { return function (a) { return a } }
function ca() { return function () { } }
function da(a) { return function (b) { this[a] = b } }
So do they use some tools to change their js files before release?
They use JavaScript minification tools like jscompress. This will reduce the filesize, speed up the user's download and reduce bandwidth costs. It also works as code obfuscation.