observer function leaks memory on the server

[doctyper]

Wrapping a component in observer() leaks memory when rendering universally. This is due to componentWillMount creating a reaction that is never disposed, since componentWillUnmount is not called on the server.

My current workaround involves avoiding wrapping a component in observer() when rendering on the server. This works, but obviously it's not an elegant solution:

import React from "react";
import {observer} from "mobx-react";
import {canUseDOM} from "exenv";

const Example = () => (<div>Example</div>);

export default (canUseDOM ? observer(Example) : Example)

An easy solution is to bail on the server on componentWillMount, though I'm not sure if there would be side-effects in doing so. Let me know if you'd like me to attempt a PR.

[mweststrate]

@doctyper not a solution, but note that that not unmounting the observer components will only create a mem leak if the observables they use live longer then the request in which you render the components. Otherwise the used observables run out of scope as well, and the components should still be GC-ed

[doctyper]

Hm, I'm not sure how accurate that statement is. We incorporated MobX into react-wildcat a few weeks ago, and within the hour we observed an enormous amount of leaked memory that was not being garbage collected.

The leak was mitigated when I added the fix to bail on the server.

[mweststrate]

@doctyper what would you think about having a global mobxReact setting, that changes this behavior on the fly? This is because trying to detect it automatically might interfer with Jest / Enzyme tests etc that are run 'server side'.

For example:
mobxReact.useServerSideRendering(true) ?

[mattruby]

I think that flag would work well.

On Wed, Nov 2, 2016 at 3:57 PM, Michel Weststrate notifications@github.com
wrote:

@doctyper https://github.com/doctyper what would you think about having
a global mobxReact setting, that changes this behavior on the fly? This is
because trying to detect it automatically might interfer with Jest / Enzyme
tests etc that are run 'server side'.

For example:
mobxReact.useServerSideRendering(true) ?

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[doctyper]

As long as it's opt-in, yes that would work well indeed.

[mweststrate]

Released as 3.5.9, call is useStaticRendering(true), which is more descriptive I think. Let us know if that doesn't solve the issue!