fix(handles): only check for matching handle id if an id exists

packages/core/src/components/Handle/Handle.vue

@@ -27,7 +27,10 @@ const { onMouseDown, onClick } = useHandle({
 
 const isConnectable = computed(() => {
   if (isString(connectable) && connectable === 'single') {
-    return !connectedEdges.value.some((edge) => edge[type.value] === nodeId && edge[`${type.value}Handle`] === handleId)
+    return !connectedEdges.value.some((edge) => {
+      const handle = edge[`${type.value}Handle`]
+      return edge[type.value] === nodeId && !!handle ? edge[`${type.value}Handle`] === handleId : true
+    })
   } else if (isFunction(connectable)) {
     return connectable(node, connectedEdges.value)
   }

packages/core/src/types/handle.ts

@@ -22,7 +22,13 @@ export type ValidConnectionFunc = (
   elements: { edges: GraphEdge[]; sourceNode: GraphNode; targetNode: GraphNode },
 ) => boolean
 
-/** set to true to allow unlimited connections, single for only one connection or use a cb function to determine connect-ability */
+/**
+ * set to true to allow unlimited connections,
+ * single for only one connection
+ * or use a cb function to determine connect-ability
+ *
+ * if set to single and the handle already has more than one connection, it will act the same as setting it to false
+ */
 export type HandleConnectable = boolean | 'single' | ((node: GraphNode, connectedEdges: GraphEdge[]) => boolean)
 
 export interface HandleProps {