Fixed some bugs caused by unbound this

src/common/graph/graphelement.ts

@@ -9,6 +9,8 @@ export class GraphElement<JSONType, HistoryType> extends SerializableItem<
 
     constructor(id = -1, graph: Graph = undefined) {
         super(id);
+        this.equals = this.equals.bind(this);
+
         this.graph = graph;
     }
 
@@ -33,6 +35,10 @@ export class GraphElement<JSONType, HistoryType> extends SerializableItem<
      * @returns True, if given object is identical.
      */
     public equals(other: GraphElement<JSONType, HistoryType>): boolean {
+        if (other == undefined) {
+            return false;
+        }
+
         return other.constructor == this.constructor && other.id == this.id;
     }
 }

src/common/graph/link.ts

@@ -37,6 +37,9 @@ export class Link
 
     constructor(source?: Node, target?: Node, graph?: Graph) {
         super(0, graph);
+
+        this.equals = this.equals.bind(this);
+
         this.source = source;
         this.target = target;
     }
@@ -94,6 +97,10 @@ export class Link
     }
 
     public equals(other: GraphElement<LinkData, SimLinkData>): boolean {
+        if (other == undefined) {
+            return false;
+        }
+
         if (other.constructor != this.constructor) {
             return false;
         }

src/editor/graph.ts

@@ -15,6 +15,10 @@ export class DynamicGraph extends Common.Graph {
         super(data);
         this.onChangeCallbacks = [];
 
+        super.deleteNode = super.deleteNode.bind(this);
+        super.deleteLink = super.deleteLink.bind(this);
+        super.deleteNodeType = super.deleteNodeType.bind(this);
+
         if (data != undefined) {
             this.history = new History<SimGraphData>(
                 this,
@@ -116,7 +120,7 @@ export class DynamicGraph extends Common.Graph {
     }
 
     public deleteLink(id: number): boolean {
-        return this.delete(id, super.deleteNode);
+        return this.delete(id, super.deleteLink);
     }
 
     getLink(