---
url: >-
  https://lit-ui-router.dev/reference/lit-ui-router-mobx/interfaces/ReactionControllerOptions.md
---
[lit-ui-router-mobx](../index.md) / ReactionControllerOptions

# Interface: ReactionControllerOptions\<T>

Defined in: [lit-ui-router-mobx/src/reaction-controller.ts:5](https://github.com/simshanith/lit-ui-router/blob/740888c2b2ba358c4dfa52a122e927df6a604b12/packages/lit-ui-router-mobx/src/reaction-controller.ts#L5)

Options for [ReactionController](../classes/ReactionController.md).

## Extended by

* [`RouterReactionControllerOptions`](RouterReactionControllerOptions.md)

## Type Parameters

| Type Parameter |
| ------ |
|  `T` |

## Properties

| Property | Type | Description | Defined in |
| ------ | ------ | ------ | ------ |
|  `equals?` | [`IEqualsComparer`](https://mobx.js.org/computeds.html#built-in-comparers)<`T`> | Comparer deciding whether the selected value changed (e.g. `compareStructural` on mobx 7, `comparer.structural` on mobx 6). Defaults to MobX's identity comparer. | [lit-ui-router-mobx/src/reaction-controller.ts:26](https://github.com/simshanith/lit-ui-router/blob/740888c2b2ba358c4dfa52a122e927df6a604b12/packages/lit-ui-router-mobx/src/reaction-controller.ts#L26) |
|  `initialValue?` | `T` | Value exposed on `.value` before the first reaction run — that is, before `hostConnected`, and on any host that renders while disconnected (SSR). Without it `.value` is `undefined` until the host connects, which is safe to render but not to read a property of. | [lit-ui-router-mobx/src/reaction-controller.ts:19](https://github.com/simshanith/lit-ui-router/blob/740888c2b2ba358c4dfa52a122e927df6a604b12/packages/lit-ui-router-mobx/src/reaction-controller.ts#L19) |
|  `onChange?` | (`value`) => `void` | Invoked (before `host.requestUpdate()`) whenever the selected value changes — and once on every host (re)connect. Use for effects such as resetting component state from route params. | [lit-ui-router-mobx/src/reaction-controller.ts:11](https://github.com/simshanith/lit-ui-router/blob/740888c2b2ba358c4dfa52a122e927df6a604b12/packages/lit-ui-router-mobx/src/reaction-controller.ts#L11) |