Walk up the prototype chain to check for .getCategory().

src/articulation.ts

@@ -13,6 +13,7 @@ import { ModifierContextState } from './modifiercontext';
 import { Builder } from './easyscore';
 import { TabNote } from './tabnote';
 import { GraceNote } from './gracenote';
+import { isTabNote } from 'typeguard';
 
 export interface ArticulationStruct {
   code?: string;
@@ -77,7 +78,7 @@ function getTopY(note: Note, textLine: number): number {
     } else {
       return Math.min(...note.getYs());
     }
-  } else if (isTabNoteCategory(note)) {
+  } else if (isTabNote(note)) {
     if (note.hasStem()) {
       if (stemDirection === Stem.UP) {
         return stemTipY;
@@ -106,7 +107,7 @@ function getBottomY(note: Note, textLine: number): number {
     } else {
       return Math.max(...note.getYs());
     }
-  } else if (isTabNoteCategory(note)) {
+  } else if (isTabNote(note)) {
     if (note.hasStem()) {
       if (stemDirection === Stem.UP) {
         return note.checkStave().getYForBottomText(textLine);
@@ -153,18 +154,12 @@ function getInitialOffset(note: Note, position: number): number {
   }
 }
 
-//#region Helper functions for checking the type of Note objects.
-// TODO: Should we replace these with isCategory from util.ts?
+// Helper function for checking if a Note object is either a StaveNote or a GraceNote.
 function isStaveOrGraceNoteCategory(note: Note): boolean {
-  const noteCategory = note.getCategory();
-  return noteCategory === StaveNote.CATEGORY || noteCategory === GraceNote.CATEGORY;
+  const category = note.getCategory();
+  return category === StaveNote.CATEGORY || category === GraceNote.CATEGORY;
 }
 
-function isTabNoteCategory(note: Note): boolean {
-  return note.getCategory() === TabNote.CATEGORY;
-}
-//#endregion
-
 /**
  * Articulations and Accents are modifiers that can be
  * attached to notes. The complete list of articulations is available in
@@ -306,7 +301,7 @@ export class Articulation extends Modifier {
 
     const stave = note.checkStave();
     const staffSpace = stave.getSpacingBetweenLines();
-    const isTab = isTabNoteCategory(note);
+    const isTab = isTabNote(note);
 
     // Articulations are centered over/under the note head.
     const { x } = note.getModifierStartXY(position, index);

src/modifiercontext.ts

@@ -39,9 +39,8 @@ export interface ModifierContextMetrics {
 export type ModifierContextMember = Modifier | StaveNote | TabNote;
 
 // To enable logging for this class. Set `Vex.Flow.ModifierContext.DEBUG` to `true`.
-function L(
-  // eslint-disable-next-line
-  ...args: any[]) {
+// eslint-disable-next-line
+function L(...args: any[]) {
   if (ModifierContext.DEBUG) log('Vex.Flow.ModifierContext', args);
 }
 
@@ -107,21 +106,23 @@ export class ModifierContext {
   }
 
   addMember(member: ModifierContextMember): this {
-    const type = member.getCategory();
-    if (!this.members[type]) this.members[type] = [];
-    this.members[type].push(member);
+    const category = member.getCategory();
+    if (!this.members[category]) {
+      this.members[category] = [];
+    }
+    this.members[category].push(member);
     member.setModifierContext(this);
     this.preFormatted = false;
     return this;
   }
 
-  getModifiers(type: string): ModifierContextMember[] {
+  getModifiers(category: string): ModifierContextMember[] {
     L('getModifiers is deprecated, use getMembers instead.');
-    return this.getMembers(type);
+    return this.getMembers(category);
   }
 
-  getMembers(type: string): ModifierContextMember[] {
-    return this.members[type];
+  getMembers(category: string): ModifierContextMember[] {
+    return this.members[category];
   }
 
   getWidth(): number {

src/ornament.ts

@@ -260,8 +260,7 @@ export class Ornament extends Modifier {
     const stemExtents = note.checkStem().getExtents();
     let y = stemDir === StaveNote.STEM_DOWN ? stemExtents.baseY : stemExtents.topY;
 
-    // TabNotes don't have stems attached to them. Tab stems are rendered
-    // outside the stave.
+    // TabNotes don't have stems attached to them. Tab stems are rendered outside the stave.
     if (note.getCategory() === TabNote.CATEGORY) {
       if (note.hasStem()) {
         if (stemDir === StaveNote.STEM_DOWN) {

src/typeguard.ts

@@ -3,23 +3,45 @@ import { TabNote } from 'tabnote';
 
 /* eslint-disable */
 type Constructor<T> = Function & { prototype: T };
+
 /**
  * Use this instead of `instanceof` as a more flexible type guard.
- * @param ClassName
- * @param obj
- * @returns true if `obj` is likely an instance of `ClassName`.
+ * @param cls a JavaScript class, such as `StaveNote`.
+ * @param obj check if this object is an instance of the provided `cls`.
+ * @param checkAncestors defaults to `true`, so we walk up the prototype chain to look for a matching `.getCategory()`.
+ *        If `false`, we do not check the superclass or other ancestors.
+ * @returns true if `obj` is an instance of `ClassName`, or has a `.getCategory()` that matches `ClassName.CATEGORY`.
  */
-export function isCategory<T>(ClassName: Constructor<T>, obj: any): obj is T {
-  // e.g., if obj is undefined or a number
-  if (typeof obj !== 'object') {
+export function isCategory<Class>(cls: Constructor<Class>, obj: any, checkAncestors: boolean = true): obj is Class {
+  // obj is NOT an instance of cls if it is:
+  // undefined, a number, a primitive string, or null.
+  if (typeof obj !== 'object' || obj === null) {
     return false;
   }
 
-  return (
-    obj instanceof ClassName ||
-    ClassName.name === obj.constructor.name ||
-    ('getCategory' in obj && obj.getCategory() === (ClassName as any).CATEGORY)
-  );
+  if (obj instanceof cls || cls.name === obj.constructor.name) {
+    return true;
+  }
+
+  // Check for the getCategory() / .CATEGORY.
+  const categoryToMatch: string | undefined = (cls as any).CATEGORY;
+  if (categoryToMatch === undefined) {
+    return false;
+  }
+
+  if (checkAncestors) {
+    // Walk up the prototype chain to look for a matching .getCategory().
+    while (obj !== null) {
+      if ('getCategory' in obj && obj.getCategory() === categoryToMatch) {
+        return true;
+      }
+      obj = Object.getPrototypeOf(obj);
+    }
+    return false;
+  } else {
+    // Do not walk up the prototype chain. Just check this object's .getCategory().
+    return 'getCategory' in obj && obj.getCategory() === categoryToMatch;
+  }
 }
 
 export function isStaveNote(obj: any): obj is StaveNote {
@@ -29,4 +51,5 @@ export function isStaveNote(obj: any): obj is StaveNote {
 export function isTabNote(obj: any): obj is TabNote {
   return isCategory<TabNote>(TabNote, obj);
 }
+
 /* eslint-enable */

src/util.ts

@@ -21,21 +21,16 @@ export function check<T>(x?: T): T {
 }
 
 /** Default log function sends all arguments to console. */
-export function log(
-  block: string,
-  // eslint-disable-next-line
-  ...args: any[]
-): void {
+// eslint-disable-next-line
+export function log(block: string, ...args: any[]): void {
   if (!args) return;
   const line = Array.prototype.slice.call(args).join(' ');
   window.console.log(block + ': ' + line);
 }
 
 /** Dump warning to console. */
-export function warn(
-  // eslint-disable-next-line
-  ...args: any[]
-): void {
+// eslint-disable-next-line
+export function warn(...args: any[]): void {
   const line = args.join(' ');
   const err = new Error();
   window.console.log('Warning: ', line, err.stack);