When XOR-encoding two strings, the resulting XOR-values of the individual characters sometimes do not result in characters that can be displayed.
Therefore one solution is to encode the result as a sequence of hex-values and then to decode these hex-values on the server side.

Javascript:

function encryptStringWithXORtoHex(input,key) {

    var c = '';

    while (key.length < input.length) {

         key += key;

    }

    for(var i=0; i<input.length; i++) {

        var value1 = input[i].charCodeAt(0);

        var value2 = key[i].charCodeAt(0);



        var xorValue = value1 ^ value2;



        var xorValueAsHexString = xorValue.toString(16);



        if (xorValueAsHexString.length < 2) {

            xorValueAsHexString = 0 + xorValueAsHexString;

        }



        c += xorValueAsHexString;

    }

    return c;

}

Java-Code:

private static String decryptStringWithXORFromHex(String input,String key) {

    StringBuilder c = new StringBuilder();

    while (key.length() < input.length()/2) {

        key += key;

    }



    for (int i=0;i<input.length();i+=2) {

        String hexValueString = input.substring(i, i+2);

        int value1 = Integer.parseInt(hexValueString, 16);

        int value2 = key.charAt(i/2);



        int xorValue = value1 ^ value2;



        c.append(Character.toString((char) xorValue));



    }

    return c.toString();

};

Example:
Encode in Javascript:

encryptStringWithXORtoHex('Encrypt This','SecretKey');

returns the string 160b00001c043f452d3b0c10

Decrypting in Java:

decryptStringWithXORFromHex(160b00001c043f452d3b0c10,SecretKey)

returns Encrypt This

Please note: the shown solution only works for characters that have a charChode value of less or equal than 255. If you want to use the solution for unicode characters (e.g. €) you will have to change the code to take care of this.