when.md

when

when(debugName?, predicate: () => boolean, effect: () => void, scope?)

when observes & runs the given predicate until it returns true. Once that happens, the given effect is executed and the autorunner is disposed. The function returns a disposer to cancel the autorunner prematurely.

This function is really useful to dispose or cancel stuff in a reactive way. For example:

class MyResource {
	constructor() {
		when(
			// once...
			() => !this.isVisible,
			// ... then
			() => this.dispose()
		);
	}

	@computed get isVisible() {
		// indicate whether this item is visible
	}

	dispose() {
		// dispose
	}
}

In MobX 1.0 this method was called autorunUntil.