[Suggestion]: imply possible undefined return value for some Graph.get*() methods in document #6784

Describe the bug / 问题描述

https://github.com/antvis/G6/blob/63f15c53be6607a73a4afb3e02b1d527ca220724/packages/g6/src/runtime/graph.ts#L558

Methods like: public getNodeData(id: ID): NodeData; should be: public getNodeData(id: ID): NodeData | undefined;.

TypeScript can't infer possible undefined in array element accesses (array[i]) like:

https://github.com/antvis/G6/blob/63f15c53be6607a73a4afb3e02b1d527ca220724/packages/g6/src/runtime/graph.ts#L575

An example fix with only getNodeData(). Can be applied to other get*() functions.

 class Graph {
   public getNodeData(): NodeData[];
-  public getNodeData(id: ID): NodeData;
+  public getNodeData(id: ID): NodeData | undefined;
   public getNodeData(ids: ID[]): NodeData[];
-  public getNodeData(id?: ID | ID[]): NodeData | NodeData[] {
+  public getNodeData(id?: ID | ID[]): NodeData | NodeData[] | undefined {
     if (id === undefined) return this.context.model.getNodeData();
     if (Array.isArray(id)) return this.context.model.getNodeData(id);
-    return this.context.model.getNodeData([id])?.[0];
+    return this.context.model.getNodeData([id])?.[0] as NodeData | undefined;
   }
 }

To check array element accesses for undefined type safety, either change them to Array.prototype.at() temporarily, or toggle noUncheckedIndexedAccess (doc, changelog, issue for making it usable).

Reproduction link / 复现链接

No response

Steps to Reproduce the Bug or Issue / 重现步骤

const nodeData = new Graph().getNodeData("non-exist-id");
console.assert(typeof nodeData !== undefined);

Version / 版本

🆕 5.x

OS / 操作系统

• macOS
• Windows
• Linux
• Others / 其他

Browser / 浏览器

• Chrome
• Edge
• Firefox
• Safari (Limited support / 有限支持)
• IE (Nonsupport / 不支持)
• Others / 其他