Choose approaches for updating an object

Say I have a simple object created by from user input:

var input = { url: 'http://example.com/', path: 'abc', user: 'adam' };

And I am to write function(s) that update url and path properties according to some business logic, there are many approaches:

A. functional

input.url = validate(input);
input.path = convert(input);

B. side-effect

update(input);

C. create a new object internally

input = process(input);

For javascript, is it always better to use the functional approach, for easier debug and speed? Or a general thought process on deciding which is more appropriate.