check for protected command names

packages/tiptap-core/src/Editor.ts

@@ -11,6 +11,7 @@ import { gapCursor } from 'prosemirror-gapcursor'
 import magicMethods from './utils/magicMethods'
 import elementFromString from './utils/elementFromString'
 import injectCSS from './utils/injectCSS'
+import getAllMethodNames from './utils/getAllMethodNames'
 import ExtensionManager from './ExtensionManager'
 import Extension from './Extension'
 import Node from './Node'
@@ -77,6 +78,10 @@ export class Editor extends EventEmitter {
       throw new Error(`tiptap: command '${name}' is already defined.`)
     }
 
+    if (getAllMethodNames(this).includes(name)) {
+      throw new Error(`tiptap: '${name}' is a protected name.`)
+    }
+    
     this.commands[name] = this.chainCommand((...args: any) => {
       return new Promise(resolve => callback(resolve, this, ...args))
     })

packages/tiptap-core/src/utils/getAllMethodNames.ts

@@ -0,0 +1,10 @@
+export default function getAllMethodNames(obj: Object) {
+  let methods = new Set()
+
+  while (obj = Reflect.getPrototypeOf(obj)) {
+    let keys = Reflect.ownKeys(obj)
+    keys.forEach((k) => methods.add(k))
+  }
+
+  return Array.from(methods)
+}