Fix: server rendering by checking document and window object are defined

[sujaykathrotia]

Server side rendering was not working as the JavaScript threw the Reference Error.
Check this issue: Hacker0x01/react-datepicker#179

[bruno12mota]

+1 for this

[ivarconr]

+1

[geekjuice]

Should Tether even execute for server-side rendering? If the assumption is that Tether shouldn't even execute on the server, would it make sense to just wrap the entire file in a function that checks that document and window are defined? For example:

let Tether;
if (typeof window !== 'undefined' && typeof document !== 'undefined') {

    if (typeof TetherBase === 'undefined') {
      throw new Error('You must include the utils.js file before tether.js');
    }

    const {
      getScrollParent,
      getBounds,
      getOffsetParent,
      extend,
      addClass,
      removeClass,
      updateClasses,
      defer,
      flush,
      getScrollBarSize
    } = TetherBase.Utils;

    ...
}

[sujaykathrotia]

I agree. Tether should not execute on the SSR. But then if someone has used object methods like setOptions, then it would throw the error. So I think it is better to check for windows and document only when we use them.

I am fine with either option though.

[sujaykathrotia]

An alternative of wrapping the entire file in an if condition, would be to check if window is defined at the top of utils.js:

if (typeof window === 'undefined') {
  return;
}

Since the output file is wrapped in a factory function, just the return statement would do the trick.

[geekjuice]

So after dwelling on this for a bit, I think the current implementation in this PR is fine for now since those are the only places where document and window gets called immediately due to them being inside IIFE.

Personally, I'm not completely satisfied with the solution, but it is a solution nonetheless and one that does seems to solve the issue well. Ideally, I would like to short-circuit the entire library when window and document are undefined, but that may require some restructuring of the library.

Thanks again for your patience 👍

[sujaykathrotia]

@geekjuice The last solution I suggested would short-circuit the entire library without restructuring of the library.