Fix SSR

[whyleee]

Fixes #1223, skips running all code in environments without window object. This is done to avoid ReferenceError: window is not defined error that happens in Node.js when importing iscroll module. Scroller functionality is not required during server-side render, but usually will be triggered on the client-side where window object is available.

Tested on our project with vue-iscroll-view, which is a wrapper Vue component for iscroll. SSR works ignoring scroller functionality and client-side works by applying scroller in mounted hook (only called on client-side), this is done by iscroll-view component.

[whyleee]

On second thought I read this w3c/IntersectionObserver#327 and it makes sense 🙂. I'm reverting to conditional module loading and closing the pull request:

import IScrollView from 'vue-iscroll-view'
const IScroll = typeof window != 'undefined' ? require('iscroll') : {}

Vue.use(IScrollView, IScroll)

The problem that I need to mix CommonJS with ES modules for this, but Webpack solves the issue for now and later SSR tools will probably become better 🙂