Use InstanceType for proper narrowing

src/@types/move-types.ts

@@ -14,21 +14,39 @@ export type * from "#app/data/moves/move";
 
 /**
  * Map of move subclass names to their respective classes.
+ * Does not include the ChargeMove subclasses. For that, use `ChargingMoveClassMap`.
+ *
+ * @privateremarks
+ * The `Never` field is necessary to ensure typescript does not improperly narrow a failed `is` guard to `never`.
+ *
+ * For example, if we did not have the never, and wrote
+ * ```
+ * function Foo(move: Move) {
+ * if (move.is("AttackMove")) {
+ *
+ * } else if (move.is("StatusMove")) { // typescript errors on the `is`, saying that `move` is `never`
+ *
+ * }
+ * ```
  */
 export type MoveClassMap = {
-  AttackMove: typeof AttackMove;
-  StatusMove: typeof StatusMove;
-  SelfStatusMove: typeof SelfStatusMove;
-  ChargingAttackMove: typeof ChargingAttackMove;
-  ChargingSelfStatusMove: typeof ChargingSelfStatusMove;
-  ChargeMove: typeof ChargingAttackMove | typeof ChargingSelfStatusMove;
+  AttackMove: AttackMove;
+  StatusMove: StatusMove;
+  SelfStatusMove: SelfStatusMove;
 };
 
+/*
+ * Without the `Never: never` field, typescript will
+ */
+
 /**
  * Union type of all move subclass names
  */
-export type MoveClass = keyof MoveClassMap;
+export type MoveKindString = "AttackMove" | "StatusMove" | "SelfStatusMove";
 
+/**
+ * Map of move attribute names to attribute instances.
+ */
 export type MoveAttrMap = {
   [K in keyof MoveAttrConstructorMap]: InstanceType<MoveAttrConstructorMap[K]>;
 };

src/data/abilities/ability.ts

@@ -2527,17 +2527,11 @@ export class AllyStatMultiplierAbAttr extends AbAttr {
  * @extends AbAttr
  */
 export class ExecutedMoveAbAttr extends AbAttr {
-  canApplyExecutedMove(
-    _pokemon: Pokemon,
-    _simulated: boolean,
-  ): boolean {
+  canApplyExecutedMove(_pokemon: Pokemon, _simulated: boolean): boolean {
     return true;
   }
 
-  applyExecutedMove(
-    _pokemon: Pokemon,
-    _simulated: boolean,
-  ): void {}
+  applyExecutedMove(_pokemon: Pokemon, _simulated: boolean): void {}
 }
 
 /**
@@ -2545,7 +2539,7 @@ export class ExecutedMoveAbAttr extends AbAttr {
  * @extends ExecutedMoveAbAttr
  */
 export class GorillaTacticsAbAttr extends ExecutedMoveAbAttr {
-  constructor(showAbility: boolean = false) {
+  constructor(showAbility = false) {
     super(showAbility);
   }
 
@@ -7773,7 +7767,7 @@ export function applyPreAttackAbAttrs(
 export function applyExecutedMoveAbAttrs(
   attrType: Constructor<ExecutedMoveAbAttr>,
   pokemon: Pokemon,
-  simulated: boolean = false,
+  simulated = false,
   ...args: any[]
 ): void {
   applyAbAttrsInternal<ExecutedMoveAbAttr>(

src/data/battle-anims.ts

@@ -446,12 +446,11 @@ export function initMoveAnim(move: MoveId): Promise<void> {
       }
     } else {
       moveAnims.set(move, null);
-      const defaultMoveAnim =
-        allMoves[move].is("AttackMove")
-          ? MoveId.TACKLE
-          : allMoves[move].is("SelfStatusMove")
-            ? MoveId.FOCUS_ENERGY
-            : MoveId.TAIL_WHIP;
+      const defaultMoveAnim = allMoves[move].is("AttackMove")
+        ? MoveId.TACKLE
+        : allMoves[move].is("SelfStatusMove")
+          ? MoveId.FOCUS_ENERGY
+          : MoveId.TAIL_WHIP;
 
       const fetchAnimAndResolve = (move: MoveId) => {
         globalScene

src/data/moves/move.ts

@@ -123,7 +123,7 @@ import { MoveEffectTrigger } from "#enums/MoveEffectTrigger";
 import { MultiHitType } from "#enums/MultiHitType";
 import { invalidAssistMoves, invalidCopycatMoves, invalidMetronomeMoves, invalidMirrorMoveMoves, invalidSleepTalkMoves } from "./invalid-moves";
 import { SelectBiomePhase } from "#app/phases/select-biome-phase";
-import { ChargingMove, MoveAttrMap, MoveAttrString, MoveClass, MoveClassMap } from "#app/@types/move-types";
+import { ChargingMove, MoveAttrMap, MoveAttrString, MoveKindString, MoveClassMap } from "#app/@types/move-types";
 import { applyMoveAttrs } from "./apply-attrs";
 import { frenzyMissFunc, getMoveTargets } from "./move-utils";
 
@@ -153,10 +153,13 @@ export default abstract class Move implements Localizable {
   /**
    * Check if the move is of the given subclass without requiring `instanceof`.
    * 
+   * ⚠️ Does _not_ work for {@linkcode ChargingAttackMove} and {@linkcode ChargingSelfStatusMove} subclasses. For those,
+   * use {@linkcode isChargingMove} instead.
+   * 
    * @param moveKind - The string name of the move to check against
    * @returns Whether this move is of the provided type.
    */
-  public abstract is<K extends keyof MoveClassMap>(moveKind: K): this is MoveClassMap[K];
+  public abstract is<K extends MoveKindString>(moveKind: K): this is MoveClassMap[K];
 
   constructor(id: MoveId, type: PokemonType, category: MoveCategory, defaultMoveTarget: MoveTarget, power: number, accuracy: number, pp: number, chance: number, priority: number, generation: number) {
     this.id = id;
@@ -976,6 +979,10 @@ export default abstract class Move implements Localizable {
 }
 
 export class AttackMove extends Move {
+  /** This field does not exist at runtime and must not be used.
+   * Its sole purpose is to ensure that typescript is able to properly narrow when the `is` method is called.
+   */
+  declare private _: never;
   override is<K extends keyof MoveClassMap>(moveKind: K): this is MoveClassMap[K] {
     return moveKind === "AttackMove";
   }
@@ -1026,21 +1033,29 @@ export class AttackMove extends Move {
 }
 
 export class StatusMove extends Move {
+  /** This field does not exist at runtime and must not be used.
+   * Its sole purpose is to ensure that typescript is able to properly narrow when the `is` method is called.
+   */
+  declare private _: never;
   constructor(id: MoveId, type: PokemonType, accuracy: number, pp: number, chance: number, priority: number, generation: number) {
     super(id, type, MoveCategory.STATUS, MoveTarget.NEAR_OTHER, -1, accuracy, pp, chance, priority, generation);
   }
 
-  override is<K extends keyof MoveClassMap>(moveKind: K): this is MoveClassMap[K] {
+  override is<K extends MoveKindString>(moveKind: K): this is MoveClassMap[K] {
     return moveKind === "StatusMove";
   }
 }
 
 export class SelfStatusMove extends Move {
+  /** This field does not exist at runtime and must not be used.
+   * Its sole purpose is to ensure that typescript is able to properly narrow when the `is` method is called.
+   */
+  declare private _: never;
   constructor(id: MoveId, type: PokemonType, accuracy: number, pp: number, chance: number, priority: number, generation: number) {
     super(id, type, MoveCategory.STATUS, MoveTarget.USER, -1, accuracy, pp, chance, priority, generation);
   }
 
-  override is<K extends keyof MoveClassMap>(moveKind: K): this is MoveClassMap[K] {
+  override is<K extends MoveKindString>(moveKind: K): this is MoveClassMap[K] {
     return moveKind === "SelfStatusMove";
   }
 }
@@ -1067,11 +1082,6 @@ function ChargeMove<TBase extends SubMove>(Base: TBase, nameAppend: string) {
       return true;
     }
 
-    override is<K extends keyof MoveClassMap>(moveKind: K): this is MoveClassMap[K] {
-      // Anything subclassing this is a charge move.
-      return moveKind === "ChargeMove" || moveKind === nameAppend || super.is(moveKind);
-    }
-
     /**
      * Sets the text to be displayed during this move's charging phase.
      * References to the user Pokemon should be written as "{USER}", and
@@ -1151,14 +1161,14 @@ export abstract class MoveAttr {
   public selfTarget: boolean;
 
   /**
-   * Returns whether this attribute is of the given type.
+   * Return whether this attribute is of the given type.
    *
    * @remarks
    * Used to avoid requring the caller to have imported the specific attribute type, avoiding circular dependencies.
    * @param attr - The attribute to check against
-   * @returns Whether the attribute is an instanceof the given type.
+   * @returns Whether the attribute is an instance of the given type.
    */
-  public is<T extends MoveAttrString>(attr: T): this is MoveAttrConstructorMap[MoveAttrString] {
+  public is<T extends MoveAttrString>(attr: T): this is MoveAttrMap[T] {
     const targetAttr = MoveAttrs[attr];
     if (!targetAttr) {
       return false;
@@ -3096,7 +3106,11 @@ export class WeatherInstantChargeAttr extends InstantChargeAttr {
 }
 
 export class OverrideMoveEffectAttr extends MoveAttr {
-  apply(user: Pokemon, target: Pokemon, move: Move, args: any[]): boolean {
+  /** This field does not exist at runtime and must not be used.
+   * Its sole purpose is to ensure that typescript is able to properly narrow when the `is` method is called.
+   */
+  declare private _: never;
+  override apply(user: Pokemon, target: Pokemon, move: Move, args: any[]): boolean {
     return true;
   }
 }
@@ -8401,7 +8415,8 @@ const MoveAttrs = Object.freeze({
   ResistLastMoveTypeAttr,
   ExposedMoveAttr,
 });
-/** Map of names  */
+
+/** Map of of move attribute names to their constructors */
 export type MoveAttrConstructorMap = typeof MoveAttrs;
 
 export const selfStatLowerMoves: MoveId[] = [];

src/phases/move-effect-phase.ts

@@ -28,7 +28,6 @@ import {
 } from "#app/data/battler-tags";
 import { BattlerTagLapseType } from "#enums/battler-tag-lapse-type";
 import type { MoveAttr } from "#app/data/moves/move";
-import { MoveEffectAttr } from "#app/data/moves/move";
 import { getMoveTargets } from "#app/data/moves/move-utils";
 import { applyFilteredMoveAttrs, applyMoveAttrs } from "#app/data/moves/apply-attrs";
 import { MoveEffectTrigger } from "#enums/MoveEffectTrigger";
@@ -746,7 +745,7 @@ export class MoveEffectPhase extends PokemonPhase {
   ): void {
     applyFilteredMoveAttrs(
       (attr: MoveAttr) =>
-        attr instanceof MoveEffectAttr &&
+        attr.is("MoveEffectAttr") &&
         attr.trigger === triggerType &&
         (isNullOrUndefined(selfTarget) || attr.selfTarget === selfTarget) &&
         (!attr.firstHitOnly || this.firstHit) &&