Add Node.splitNodeAfter, to allow for exact undo of joinNode

src/models/node.js

@@ -1259,7 +1259,7 @@ const Node = {
   /**
    * Split a node by `path` at `offset`.
    *
-   * @param {String} path
+   * @param {Array} path
    * @param {Number} offset
    * @return {Node}
    */
@@ -1312,6 +1312,40 @@ const Node = {
     return base
   },
 
+  /**
+   * Split a node by `path` after 'count' children.
+   * Does not work on Text nodes. Use `Node.splitNode` to split text nodes as well.
+   *
+   * @param {Array} path
+   * @param {Number} count
+   * @return {Node}
+   */
+
+  splitNodeAfter(path, count) {
+    let base = this
+    let node = base.assertPath(path)
+    if (node.kind === 'text') throw new Error('Cannot split text node at index. Use Node.splitNode at offset instead')
+    const { nodes } = node
+
+    let parent = base.getParent(node.key)
+    const isParent = base == parent
+
+    const oneNodes = nodes.take(count)
+    const twoNodes = nodes.skip(count)
+
+    const one = node.merge({ nodes: oneNodes })
+    const two = node.merge({ nodes: twoNodes, key: uid() })
+
+
+    const nodeIndex = parent.nodes.indexOf(node)
+    parent = parent.removeNode(nodeIndex)
+    parent = parent.insertNode(nodeIndex, two)
+    parent = parent.insertNode(nodeIndex, one)
+
+    base = isParent ? parent : base.updateDescendant(parent)
+    return base
+  },
+
   /**
    * Split the block nodes at a `range`, to optional `height`.
    *

src/transforms/apply-operation.js

@@ -392,15 +392,27 @@ function setSelection(state, operation) {
  *
  * @param {State} state
  * @param {Object} operation
+ *   @param {Array} operation.path The path of the node to split
+ *   @param {Number} operation.offset (optional) Split using a relative offset
+ *   @param {Number} operation.count (optional) Split after `count`
+ *   children. Cannot be used in combination with offset.
  * @return {State}
  */
 
 function splitNode(state, operation) {
-  const { path, offset } = operation
+  const { path, offset, count } = operation
   const { document } = state
 
+  if (offset === undefined) {
+    return state.merge({
+      document: document.splitNodeAfter(path, count)
+      // No need to update selection
+    })
+  }
+
+  else {
     // Update document
-  const newDocument = document.splitNode(path, offset)
+    let newDocument = document.splitNode(path, offset)
 
     // Update selection
     let { selection } = state
@@ -452,3 +464,4 @@ function splitNode(state, operation) {
     })
     return state
   }
+}

src/transforms/operations.js

@@ -106,13 +106,26 @@ export function joinNodeOperation(transform, path, withPath) {
   const { state } = transform
   const { document } = state
   const node = document.assertPath(withPath)
+
+  let inverse
+  if (node.kind === 'text') {
     const offset = node.length
 
-  const inverse = [{
+    inverse = [{
       type: 'split_node',
       path: withPath,
       offset,
     }]
+  } else {
+    // The number of children after which we split
+    const count = node.nodes.count()
+
+    inverse = [{
+      type: 'split_node',
+      path: withPath,
+      count,
+    }]
+  }
 
   const operation = {
     type: 'join_node',