# Updating mutable inside function

**URL:** <https://talk.observablehq.com/t/updating-mutable-inside-function/5692>\
**Category:** Help\
**Created:** [October 15, 2021, 12:49pm UTC](https://talk.observablehq.com/t/updating-mutable-inside-function/5692 "2021-10-15T12:49:21Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![jerryjappinen](https://yyz2.discourse-cdn.com/flex030/user_avatar/talk.observablehq.com/jerryjappinen/32/9133_2.png) [@jerryjappinen](https://talk.observablehq.com/u/jerryjappinen)\
**Post date:** [October 15, 2021, 12:49pm UTC](https://talk.observablehq.com/t/updating-mutable-inside-function/5692/1 "2021-10-15T12:49:22Z")

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**Demo notebook here** : [https://observablehq.com/@jerryjappinen/mutable-fetch-test](https://observablehq.com/@jerryjappinen/mutable-fetch-test)

**What I want to do**

I’m querying a paginated list of users. I want to have all users in one object by ID.

I have a `mutable allUsers = ({})` object. Then, in my `async fetchUsers` I update `allUsers` once I get a response.

**Problem** : I get an endless loop of requests when updating `mutable allUsers` inside `fetchUsers`. My guess is that it throws off Observable’s change detection and it thinks `fetchUsers` need to be run every time `allUsers` is updated.

This has to be dynamic. I do not want to hardcode a variable for every fetch and combine those into allUsers. Order fetching is also important: every time I query the API, any users returned is considered to be the newest version of this object, so it should override a previously included object with the same ID.

**Questions**

- Can this be made to work?
- Is there a more “observable” way of doing this?

I’ve tried to play with workarounds (using yield etc.) but have not been able to get this working.

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**Author:** ![duaneatat](https://yyz2.discourse-cdn.com/flex030/user_avatar/talk.observablehq.com/duaneatat/32/5654_2.png) [@duaneatat](https://talk.observablehq.com/u/duaneatat)\
**Post date:** [October 15, 2021, 2:12pm UTC](https://talk.observablehq.com/t/updating-mutable-inside-function/5692/2 "2021-10-15T14:12:17Z")

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Hi Jerry,

It looks like this is because in the object spread you reference `allUsers`, which does make the observable runtime consider that cell to be downstream of `allUsers` and reevaluates the cell when `allUsers` changes. You can fix this by referencing `mutable allUsers` instead which removes that reactivity:

```auto
mutable allUsers = { ...mutable allUsers, ...responseUsersById }

```

instead of

```auto
mutable allUsers = { ...allUsers, ...responseUsersById }

```

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<div class="post-metadata">

**Author:** ![jerryjappinen](https://yyz2.discourse-cdn.com/flex030/user_avatar/talk.observablehq.com/jerryjappinen/32/9133_2.png) [@jerryjappinen](https://talk.observablehq.com/u/jerryjappinen)\
**Post date:** [October 15, 2021, 2:23pm UTC](https://talk.observablehq.com/t/updating-mutable-inside-function/5692/3 "2021-10-15T14:23:28Z")

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This is indeed it. Still had not quite grasped this with `mutable`. Thanks for the quick response @duaneatat !

I’ve updated the demo notebook with working code.