> For AI agents: the complete documentation index is available at https://nhanbe.id.vn/llms.txt, the full documentation bundle is available at https://nhanbe.id.vn/llms-full.txt.

# Prototype

## Overview

Create new objects by copying an existing instance (the prototype).

## When to use

- Object creation is expensive or complex.
- You need many similar instances with small variations.

## Java example

```java
class Report implements Cloneable {
    private String title;
    private List<String> sections;

    Report(String title, List<String> sections) {
        this.title = title;
        this.sections = new ArrayList<>(sections);
    }

    public Report copy() {
        return new Report(title, sections);
    }
}
```

## TypeScript example

```ts
type Report = {
  title: string;
  sections: string[];
};

const prototype: Report = { title: "Monthly", sections: ["Summary", "KPIs"] };
const copy: Report = { ...prototype, sections: [...prototype.sections] };
```

## Pros and cons

Pros:

- Fast creation via cloning.
- Avoids complex constructor logic.

Cons:

- Deep copy can be tricky.
- Clones may share mutable state if not careful.

## Common pitfalls

- Shallow copy of nested objects.
- Mutating shared references after cloning.

## Related patterns

- [Builder](https://nhanbe.id.vn/design-patterns/creational/builder.md)
- [Factory Method](https://nhanbe.id.vn/design-patterns/creational/factory-method.md)