docs: tweak createSubscriber explanation

Rich-Harris · Rich-Harris · commit f45c37f2b65c · 2025-07-16T13:05:37.000-04:00
diff --git a/packages/svelte/src/reactivity/create-subscriber.js b/packages/svelte/src/reactivity/create-subscriber.js
@@ -6,10 +6,13 @@ import { DEV } from 'esm-env';
 import { queue_micro_task } from '../internal/client/dom/task.js';
 
 /**
- * Returns a `subscribe` function that, if called in an effect (including expressions in the template),
- * calls its `start` callback with an `update` function. Whenever `update` is called, the effect re-runs.
+ * Returns a `subscribe` function that integrates external event-based systems with Svelte's reactivity.
+ * It's particularly useful for integrating with web APIs like `MediaQuery`, `IntersectionObserver`, or `WebSocket`.
  *
- * If `start` returns a function, it will be called when the effect is destroyed.
+ * If `subscribe` is called inside an effect (including indirectly, for example inside a getter),
+ * the `start` callback will be called with an `update` function. Whenever `update` is called, the effect re-runs.
+ *
+ * If `start` returns a cleanup function, it will be called when the effect is destroyed.
  *
  * If `subscribe` is called in multiple effects, `start` will only be called once as long as the effects
  * are active, and the returned teardown function will only be called when all effects are destroyed.
@@ -37,6 +40,7 @@ import { queue_micro_task } from '../internal/client/dom/task.js';
  * 	}
  *
  * 	get current() {
+ * 		// This makes the getter reactive, if read in an effect
  * 		this.#subscribe();
  *
  * 		// Return the current state of the query, whether or not we're in an effect

Original file line number	Diff line number	Diff line change
`@@ -6,10 +6,13 @@ import { DEV } from 'esm-env';`
`6`	`6`	`import { queue_micro_task } from '../internal/client/dom/task.js';`
`7`	`7`
`8`	`8`	`/**`
`9`		- * Returns a `subscribe` function that, if called in an effect (including expressions in the template),
`10`		- * calls its `start` callback with an `update` function. Whenever `update` is called, the effect re-runs.
	`9`	+ * Returns a `subscribe` function that integrates external event-based systems with Svelte's reactivity.
	`10`	+ * It's particularly useful for integrating with web APIs like `MediaQuery`, `IntersectionObserver`, or `WebSocket`.
`11`	`11`	`*`
`12`		- * If `start` returns a function, it will be called when the effect is destroyed.
	`12`	+ * If `subscribe` is called inside an effect (including indirectly, for example inside a getter),
	`13`	+ * the `start` callback will be called with an `update` function. Whenever `update` is called, the effect re-runs.
	`14`	`+ *`
	`15`	+ * If `start` returns a cleanup function, it will be called when the effect is destroyed.
`13`	`16`	`*`
`14`	`17`	* If `subscribe` is called in multiple effects, `start` will only be called once as long as the effects
`15`	`18`	`* are active, and the returned teardown function will only be called when all effects are destroyed.`
`@@ -37,6 +40,7 @@ import { queue_micro_task } from '../internal/client/dom/task.js';`
`37`	`40`	`* }`
`38`	`41`	`*`
`39`	`42`	`* get current() {`
	`43`	`+ * // This makes the getter reactive, if read in an effect`
`40`	`44`	`* this.#subscribe();`
`41`	`45`	`*`
`42`	`46`	`* // Return the current state of the query, whether or not we're in an effect`