fix(router): prevent memory leaks by removing app references

[posva]

Fix #2639

Hey, @tmorehouse, I refactored the tests and reverted the code added to the if because I couldn't see why we would override the main app. Could you take a look please?

[tmorehouse]

I'll take a look here in a bit.

[tmorehouse]

With this.app being set to null (if all apps are cleared out), this early return doesn't happen, and the code below it will be executed again.

Will that be an issue? IF so, maybe a flag needs to be set so that the following code is not executed a second time.

[posva]

but this is called when a router is injected in a created component, it's only executed once per root instance

[tmorehouse]

Doesn't init get called for each app instance, as it is how the apps get added to this.apps array:

  init (app: any /* Vue component instance */) {
    process.env.NODE_ENV !== 'production' && assert(
      install.installed,
      `not installed. Make sure to call \`Vue.use(VueRouter)\` ` +
      `before creating root instance.`
    )

    this.apps.push(app)

[posva]

yes, but once per root instance

[tmorehouse]

Ah, correct... so it should be good.