Feature: Add selector subscriptions #551
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rekmarks
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rekmarks
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Aug 3, 2021
src/ControllerMessenger.ts
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| for (const [handler, selector] of subscribers.entries()) { | ||
| if (selector) { | ||
| const newValue = selector(...payload); | ||
|
|
||
| if (newValue !== this.eventPayloadCache.get(handler)) { | ||
| this.eventPayloadCache.set(handler, newValue); | ||
| handler(newValue); | ||
| } | ||
| } else { | ||
| handler(...payload); | ||
| } |
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This is a pre-existing issue so I'm disinclined to deal with it here, but, if a handler or selector throws, any remaining handlers will not be called. Should we somehow catch errors from handlers and/or selectors?
cc: @Gudahtt
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I suppose we could just repeat the trick we use in safe-event-emitter: https://github.com/MetaMask/safe-event-emitter/blob/faf5620ac17ac6d32d8dd00ba0c3ffd9247ee6cf/index.ts/#L8-L17
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MajorLift
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This non-breaking PR adds [`reselect`](https://npmjs.com/package/reselect)-style selectors as an optional parameter to controller messenger event subscriptions. We call subscriptions with selectors **selector subscriptions**. This enables subscribing to subsets of large event payloads, for example `*:stateChange` events. ```typescript // ControllerMessenger.subscribe selector signature subscribe<E extends Event['type'], V>( eventType: E, handler: (nextValue: V, previousValue: V | undefined) => void, selector: (payload: ExtractEventPayload<Event, E>) => V, ): void; ``` When a selector subscription is triggered, the corresponding selector is passed the entire event payload, and returns a single value. If the value has changed since the last occurrence of the event, the handler is called with the new value and the previous value, or `undefined` if no previous value exists. Since controller state is immutable, the event handler can efficiently diff the selector return values and trigger other logic dependent on changes to subsets of complex event payloads (e.g., other events). This feature is motivated by our frequent need to subscribe to controller substate(s). Every controller has a generic `*:stateChange` event, but parsing that state is often error-prone and/or annoying. By adding selector subscriptions, we can performantly parse complex controller state in one place, and emit more specific events as necessary. This implementation was chosen due to our existing widespread use of selectors in our UIs, and in order to avoid the introduction of querying DSLs such as JSONPath and GraphQL at this time. In addition to adding selector subscriptions, this PR modifies an error messages and does some minor, non-breaking type touchup. Closes #528
MajorLift
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Oct 11, 2023
This non-breaking PR adds [`reselect`](https://npmjs.com/package/reselect)-style selectors as an optional parameter to controller messenger event subscriptions. We call subscriptions with selectors **selector subscriptions**. This enables subscribing to subsets of large event payloads, for example `*:stateChange` events. ```typescript // ControllerMessenger.subscribe selector signature subscribe<E extends Event['type'], V>( eventType: E, handler: (nextValue: V, previousValue: V | undefined) => void, selector: (payload: ExtractEventPayload<Event, E>) => V, ): void; ``` When a selector subscription is triggered, the corresponding selector is passed the entire event payload, and returns a single value. If the value has changed since the last occurrence of the event, the handler is called with the new value and the previous value, or `undefined` if no previous value exists. Since controller state is immutable, the event handler can efficiently diff the selector return values and trigger other logic dependent on changes to subsets of complex event payloads (e.g., other events). This feature is motivated by our frequent need to subscribe to controller substate(s). Every controller has a generic `*:stateChange` event, but parsing that state is often error-prone and/or annoying. By adding selector subscriptions, we can performantly parse complex controller state in one place, and emit more specific events as necessary. This implementation was chosen due to our existing widespread use of selectors in our UIs, and in order to avoid the introduction of querying DSLs such as JSONPath and GraphQL at this time. In addition to adding selector subscriptions, this PR modifies an error messages and does some minor, non-breaking type touchup. Closes #528
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Closes #528
This non-breaking PR adds
reselect-style selectors as an optional parameter to controller messenger event subscriptions. We call subscriptions with selectors selector subscriptions. This enables subscribing to subsets of large event payloads, for example*:stateChangeevents.When a selector subscription is triggered, the corresponding selector is passed the entire event payload, and returns a single value. If the value has changed since the last occurrence of the event, the handler is called with the new value and the previous value, or
undefinedif no previous value exists. Since controller state is immutable, the event handler can efficiently diff the selector return values and trigger other logic dependent on changes to subsets of complex event payloads (e.g., other events).This feature is motivated by our frequent need to subscribe to controller substate(s). Every controller has a generic
*:stateChangeevent, but parsing that state is often error-prone and/or annoying. By adding selector subscriptions, we can performantly parse complex controller state in one place, and emit more specific events as necessary. This implementation was chosen due to our existing widespread use of selectors in our UIs, and in order to avoid the introduction of querying DSLs such as JSONPath and GraphQL at this time.In addition to adding selector subscriptions, this PR modifies an error messages and does some minor, non-breaking type touchup.