Question

var Obj = {};
Obj.ID = e.row.ID;
Obj.firstName = e.row.firstName;
Obj.lastName = e.row.lastName;

This is my object, and i save this object in a file. now before saving into file, i want to encrypt it and save and while reading i want to decrypt and read.

var newFile = FileSystemPath;
newFile.write(JSON.stringify(object));

1. Should i encrypt the object before stringifying it or after it.
2. What are the ways to encrypt an object in javascript. Any examples
   would be great.

Answer 1

You can’t really encrypt objects, but you can encrypt strings, so you should probably first do a object serialization (JSON.stringify) and then encrypt it with a symmetric encryption algorithm so you would be able to decode the object later.
I can’t really provide a good example, because javascript will always have serious security problems (being a client-side programming language), and even if you try a rather complex algorithm (such as AES) it will still be vulnerable, because the user can just see your source code, thus see your encription/decription algorithms.
If you just want to alter the string a bit so it can’t be deciphered on the first look, you can simply use some built-in javascript methods (such as encodeURI/decodeURI) or you can do some character replacements or even use salts.

Here’s a sample demo of how you can “encrypt” an object :

function encrypt(o, salt) {
    o = JSON.stringify(o).split('');
    for(var i = 0, l = o.length; i < l; i++)
        if(o[i] == '{')
            o[i] = '}';
        else if(o[i] == '}')
            o[i] = '{';
    return encodeURI(salt + o.join(''));
}

 function decrypt(o, salt) {
    o = decodeURI(o);
    if(salt && o.indexOf(salt) != 0)
        throw new Error('object cannot be decrypted');
    o = o.substring(salt.length).split('');
    for(var i = 0, l = o.length; i < l; i++)
        if(o[i] == '{')
            o[i] = '}';
        else if(o[i] == '}')
            o[i] = '{';
    return JSON.parse(o.join(''));
}

var obj = {
    key : 'value',
    3 : 1
};
var salt = "some string here";
var encrypted = encrypt(obj, salt);
var decrypted = decrypt(encripted, salt);

Of course, this is just an example and you should modify it in order to encrypt more complex objects, where you need to encrypt functions, or where the object has circular references.