diff --git a/codes/javascript/chapter_graph/graph_adjacency_list.js b/codes/javascript/chapter_graph/graph_adjacency_list.js
index ec7567c3c..f3daaeb17 100644
--- a/codes/javascript/chapter_graph/graph_adjacency_list.js
+++ b/codes/javascript/chapter_graph/graph_adjacency_list.js
@@ -46,7 +46,8 @@ class GraphAdjList {
         if (
             !this.adjList.has(vet1) ||
             !this.adjList.has(vet2) ||
-            vet1 === vet2
+            vet1 === vet2 ||
+            this.adjList.get(vet1).indexOf(vet2) === -1
         ) {
             throw new Error('Illegal Argument Exception');
         }
diff --git a/codes/typescript/chapter_graph/graph_adjacency_list.ts b/codes/typescript/chapter_graph/graph_adjacency_list.ts
index 4c7692312..c928e72e4 100644
--- a/codes/typescript/chapter_graph/graph_adjacency_list.ts
+++ b/codes/typescript/chapter_graph/graph_adjacency_list.ts
@@ -46,7 +46,8 @@ class GraphAdjList {
         if (
             !this.adjList.has(vet1) ||
             !this.adjList.has(vet2) ||
-            vet1 === vet2
+            vet1 === vet2 ||
+            this.adjList.get(vet1).indexOf(vet2) === -1
         ) {
             throw new Error('Illegal Argument Exception');
         }
diff --git a/zh-hant/codes/javascript/chapter_graph/graph_adjacency_list.js b/zh-hant/codes/javascript/chapter_graph/graph_adjacency_list.js
index 6b7ff8c71..6e50bad47 100644
--- a/zh-hant/codes/javascript/chapter_graph/graph_adjacency_list.js
+++ b/zh-hant/codes/javascript/chapter_graph/graph_adjacency_list.js
@@ -46,7 +46,8 @@ class GraphAdjList {
         if (
             !this.adjList.has(vet1) ||
             !this.adjList.has(vet2) ||
-            vet1 === vet2
+            vet1 === vet2 ||
+            this.adjList.get(vet1).indexOf(vet2) === -1
         ) {
             throw new Error('Illegal Argument Exception');
         }
diff --git a/zh-hant/codes/typescript/chapter_graph/graph_adjacency_list.ts b/zh-hant/codes/typescript/chapter_graph/graph_adjacency_list.ts
index 13c76a1e5..bd137fd84 100644
--- a/zh-hant/codes/typescript/chapter_graph/graph_adjacency_list.ts
+++ b/zh-hant/codes/typescript/chapter_graph/graph_adjacency_list.ts
@@ -46,7 +46,8 @@ class GraphAdjList {
         if (
             !this.adjList.has(vet1) ||
             !this.adjList.has(vet2) ||
-            vet1 === vet2
+            vet1 === vet2 ||
+            this.adjList.get(vet1).indexOf(vet2) === -1
         ) {
             throw new Error('Illegal Argument Exception');
         }