[Bug] Fix drag link from input to output (#859)

Resolves https://github.com/Comfy-Org/litegraph.js/issues/858

src/canvas/ToOutputRenderLink.ts

@@ -45,7 +45,7 @@ export class ToOutputRenderLink implements RenderLink {
 
   connectToOutput(node: LGraphNode, output: INodeOutputSlot, events: LinkConnectorEventTarget) {
     const { node: inputNode, fromSlot, fromReroute } = this
-    if (inputNode) return
+    if (!inputNode) return
 
     const newLink = node.connectSlots(output, inputNode, fromSlot, fromReroute?.id)
     events.dispatch("link-created", newLink)

test/ToOutputRenderLink.test.ts

@@ -0,0 +1,92 @@
+import { describe, expect, it, vi } from "vitest"
+
+import { ToOutputRenderLink } from "@/canvas/ToOutputRenderLink"
+import { LinkDirection } from "@/types/globalEnums"
+
+describe("ToOutputRenderLink", () => {
+  describe("connectToOutput", () => {
+    it("should return early if inputNode is null", () => {
+      // Setup
+      const mockNetwork = {}
+      const mockFromSlot = {}
+      const mockNode = { id: "test-id", inputs: [mockFromSlot], getInputPos: vi.fn().mockReturnValue([0, 0]) }
+
+      const renderLink = new ToOutputRenderLink(
+        mockNetwork as any,
+        mockNode as any,
+        mockFromSlot as any,
+        undefined,
+        LinkDirection.CENTER,
+      )
+
+      // Override the node property to simulate null case
+      Object.defineProperty(renderLink, "node", {
+        value: null,
+      })
+
+      const mockTargetNode = {
+        connectSlots: vi.fn(),
+      }
+      const mockEvents = {
+        dispatch: vi.fn(),
+      }
+
+      // Act
+      renderLink.connectToOutput(
+        mockTargetNode as any,
+        {} as any,
+        mockEvents as any,
+      )
+
+      // Assert
+      expect(mockTargetNode.connectSlots).not.toHaveBeenCalled()
+      expect(mockEvents.dispatch).not.toHaveBeenCalled()
+    })
+
+    it("should create connection and dispatch event when inputNode exists", () => {
+      // Setup
+      const mockNetwork = {}
+      const mockFromSlot = {}
+      const mockNode = {
+        id: "test-id",
+        inputs: [mockFromSlot],
+        getInputPos: vi.fn().mockReturnValue([0, 0]),
+      }
+
+      const renderLink = new ToOutputRenderLink(
+        mockNetwork as any,
+        mockNode as any,
+        mockFromSlot as any,
+        undefined,
+        LinkDirection.CENTER,
+      )
+
+      const mockNewLink = { id: "new-link" }
+      const mockTargetNode = {
+        connectSlots: vi.fn().mockReturnValue(mockNewLink),
+      }
+      const mockEvents = {
+        dispatch: vi.fn(),
+      }
+
+      // Act
+      renderLink.connectToOutput(
+        mockTargetNode as any,
+        {} as any,
+        mockEvents as any,
+      )
+
+      // Assert
+      expect(mockTargetNode.connectSlots).toHaveBeenCalledWith(
+        expect.anything(),
+        mockNode,
+        mockFromSlot,
+        undefined,
+      )
+      expect(mockEvents.dispatch).toHaveBeenCalledWith(
+        "link-created",
+        mockNewLink,
+      )
+    })
+  })
+})