Harden split_node operation (#6043)

Author: 12joan

packages/slate/src/interfaces/transforms/general.ts

@@ -256,9 +256,7 @@ export const GeneralTransforms: GeneralTransforms = {
               throw new Error(`Cannot set the "${key}" property of nodes!`)
             }
 
-            const value = Object.hasOwn(newProperties, key)
-              ? newProperties[<keyof Node>key]
-              : undefined
+            const value = newProperties[<keyof Node>key]
 
             // Make sure we're not setting `then` to a function, since this will
             // cause the node to be treated as a Promise-like object, which can
@@ -374,7 +372,6 @@ export const GeneralTransforms: GeneralTransforms = {
               text: before,
             }
             nextNode = {
-              ...(properties as Partial<Text>),
               text: after,
             }
           } else {
@@ -385,11 +382,32 @@ export const GeneralTransforms: GeneralTransforms = {
               children: before,
             }
             nextNode = {
-              ...(properties as Partial<Element>),
               children: after,
             }
           }
 
+          for (const key in properties) {
+            if (NON_SETTABLE_NODE_PROPERTIES.includes(key)) {
+              throw new Error(`Cannot set the "${key}" property of nodes!`)
+            }
+
+            const value = properties[<keyof Node>key]
+
+            // Make sure we're not setting `then` to a function, since this will
+            // cause the node to be treated as a Promise-like object, which can
+            // cause unexpected behaviour when returning the node from async
+            // functions.
+            if (key === 'then' && typeof value === 'function') {
+              throw new Error(
+                'Cannot set the "then" property of a node to a function'
+              )
+            }
+
+            if (value != null) {
+              nextNode[<keyof Node>key] = value
+            }
+          }
+
           return replaceChildren(children, index, 1, newNode, nextNode)
         })