how to use rsa in js code example

Example: Encryption RSA, JavaScript

<script type="text/javascript">
    $(function () {

        //Change the key size value for new keys
        $(".change-key-size").each(function (index, value) {
            var el = $(value);
            var keySize = el.attr('data-value');
            el.click(function (e) {
                var button = $('#key-size');
                button.attr('data-value', keySize);
                button.html(keySize + ' bit <span class="caret"></span>');
                e.preventDefault();
            });
        });

        // Execute when they click the button.
        $('#execute').click(function () {

            // Create the encryption object.
            var crypt = new JSEncrypt();

            // Set the private.
            crypt.setPrivateKey($('#privkey').val());
            //return;
            // If no public key is set then set it here...
            var pubkey = $('#pubkey').val();
            if (!pubkey) {
                $('#pubkey').val(crypt.getPublicKey());
            }

            // Get the input and crypted values.
            var input = $('#input').val();
            var crypted = $('#crypted').val();

            // Alternate the values.
            if (input) {
                $('#crypted').val(crypt.encrypt(input));
                $('#input').val('');
            }
            else if (crypted) {
                var decrypted = crypt.decrypt(crypted);
                if (!decrypted)
                    decrypted = 'This is a test!';
                $('#input').val(decrypted);
                $('#crypted').val('');
            }
        });

        var generateKeys = function () {
            var sKeySize = $('#key-size').attr('data-value');
            var keySize = parseInt(sKeySize);
            var crypt = new JSEncrypt({ default_key_size: keySize });
            var async = $('#async-ck').is(':checked');
            var dt = new Date();
            var time = -(dt.getTime());
            if (async) {
                $('#time-report').text('.');
                var load = setInterval(function () {
                    var text = $('#time-report').text();
                    $('#time-report').text(text + '.');
                }, 500);
                crypt.getKey(function () {
                    clearInterval(load);
                    dt = new Date();
                    time += (dt.getTime());
                    $('#time-report').text('Generated in ' + time + ' ms');
                    $('#privkey').val(crypt.getPrivateKey());
                    $('#pubkey').val(crypt.getPublicKey());
                });
                return;
            }
            crypt.getKey();
            dt = new Date();
            time += (dt.getTime());
            $('#time-report').text('Generated in ' + time + ' ms');
            $('#privkey').val(crypt.getPrivateKey());
            $('#pubkey').val(crypt.getPublicKey());
        };

        // If they wish to generate new keys.
        $('#generate').click(generateKeys);
        generateKeys();
    });
</script>