feat(commands): add joinUp and joinDown command & refactor join command code

docs/api/commands/join-down.md

@@ -0,0 +1,8 @@
+# joinDown
+The `joinDown` command joins the selected block, or if there is a text selection, the closest ancestor block of the selection that can be joined, with the sibling below it. [See also](https://prosemirror.net/docs/ref/#commands.joinDown)
+
+## Usage
+```js
+editor.commands.joinDown()
+```
+

docs/api/commands/join-up.md

@@ -0,0 +1,8 @@
+# joinUp
+The `joinUp` command joins the selected block, or if there is a text selection, the closest ancestor block of the selection that can be joined, with the sibling above it. [See also](https://prosemirror.net/docs/ref/#commands.joinUp)
+
+## Usage
+```js
+editor.commands.joinUp()
+```
+

packages/core/src/commands/index.ts

@@ -15,8 +15,7 @@ export * from './focus'
 export * from './forEach'
 export * from './insertContent'
 export * from './insertContentAt'
-export * from './joinBackward'
-export * from './joinForward'
+export * from './join'
 export * from './keyboardShortcut'
 export * from './lift'
 export * from './liftEmptyBlock'

packages/core/src/commands/join.ts

@@ -0,0 +1,50 @@
+import {
+  joinBackward as originalJoinBackward, joinDown as originalJoinDown, joinForward as originalJoinForward, joinUp as originalJoinUp,
+} from 'prosemirror-commands'
+
+import { RawCommands } from '../types'
+
+declare module '@tiptap/core' {
+  interface Commands<ReturnType> {
+    joinUp: {
+      /**
+       * Join two nodes Up.
+       */
+      joinUp: () => ReturnType,
+    }
+    joinDown: {
+      /**
+       * Join two nodes Down.
+       */
+      joinDown: () => ReturnType,
+    }
+    joinBackward: {
+      /**
+       * Join two nodes Backwards.
+       */
+      joinBackward: () => ReturnType,
+    }
+    joinForward: {
+      /**
+       * Join two nodes Forwards.
+       */
+      joinForward: () => ReturnType,
+    }
+  }
+}
+
+export const joinUp: RawCommands['joinUp'] = () => ({ state, dispatch }) => {
+  return originalJoinUp(state, dispatch)
+}
+
+export const joinDown: RawCommands['joinDown'] = () => ({ state, dispatch }) => {
+  return originalJoinDown(state, dispatch)
+}
+
+export const joinBackward: RawCommands['joinBackward'] = () => ({ state, dispatch }) => {
+  return originalJoinBackward(state, dispatch)
+}
+
+export const joinForward: RawCommands['joinForward'] = () => ({ state, dispatch }) => {
+  return originalJoinForward(state, dispatch)
+}