Stego.js

var revealJS = function(s) {
    var hexAlphabet = Array.apply(null, {
        length: 10
    }).map(Number.call, Number).concat('abcdef'.split(''));
    var codes = [8289, 8204, 8205, 8206, 8207, 8234, 8235, 8236, 8237, 8238, 8298, 8299, 8300, 8301, 8302, 8303];
  
    return s.match(/(.{4})/g).map(function(b) {
        return b.split('').map(function(i) {
            return hexAlphabet[codes.indexOf(i.charCodeAt())]
        })
    }).map(function(c) {
        return String.fromCharCode(0 + "x" + c.join(''))
    }).join('')
}

var invisibleJS = function(s) {
    return s.replace(/./g, function(b) {
        var code = '0000' + b.charCodeAt().toString(16);
        code = code.substring(code.length - 4);
        return String.fromCharCode.apply(String, code.split('').map(function(a) {
            hexAlphabet = Array.apply(null, {
                length: 10
            }).map(Number.call, Number).map(function(n) {
                return n.toString();
            }).concat('abcdef'.split(''));
            codes = [8289, 8204, 8205, 8206, 8207, 8234, 8235, 8236, 8237, 8238, 8298, 8299, 8300, 8301, 8302, 8303];
            var idx = hexAlphabet.indexOf(a);
            return codes[idx]
        }))
    })
}