# ?: 可选属性

有时我们希望不要完全匹配一个形状，那么可以用可选属性：

```typescript
interface Person {
    name: string;
    age?: number;
}

let tom: Person = {
    name: 'Tom'
};
```

```typescript
interface Person {
    name: string;
    age?: number;
}

let tom: Person = {
    name: 'Tom',
    age: 25
};
```

可选属性的含义是该属性可以不存在。


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# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://mm.ricky.moe/javascript/typescript/shi-yong/ke-xuan-shu-xing.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.