chore: simplify is_dirty (#17444)

* chore: simplify is_dirty

* tidy up

packages/svelte/src/internal/client/reactivity/effects.js

@@ -328,7 +328,7 @@ export function legacy_pre_effect_reset() {
 
 			// If the effect is CLEAN, then make it MAYBE_DIRTY. This ensures we traverse through
 			// the effects dependencies and correctly ensure each dependency is up-to-date.
-			if ((effect.f & CLEAN) !== 0) {
+			if ((effect.f & CLEAN) !== 0 && effect.deps !== null) {
 				set_signal_status(effect, MAYBE_DIRTY);
 			}
 

packages/svelte/src/internal/client/runtime.js

@@ -166,21 +166,18 @@ export function is_dirty(reaction) {
 	}
 
 	if ((flags & MAYBE_DIRTY) !== 0) {
-		var dependencies = reaction.deps;
+		var dependencies = /** @type {Value[]} */ (reaction.deps);
+		var length = dependencies.length;
 
-		if (dependencies !== null) {
-			var length = dependencies.length;
+		for (var i = 0; i < length; i++) {
+			var dependency = dependencies[i];
 
-			for (var i = 0; i < length; i++) {
-				var dependency = dependencies[i];
-
-				if (is_dirty(/** @type {Derived} */ (dependency))) {
-					update_derived(/** @type {Derived} */ (dependency));
-				}
+			if (is_dirty(/** @type {Derived} */ (dependency))) {
+				update_derived(/** @type {Derived} */ (dependency));
+			}
 
-				if (dependency.wv > reaction.wv) {
-					return true;
-				}
+			if (dependency.wv > reaction.wv) {
+				return true;
 			}
 		}